Lake Dunstan – Guide to Fishing Lake Dunstan
by Dick Marquand
Lake Dunstan is New Zealand’s most recent lake formed for the purpose of hydro-electric power generation. The Clyde Dam is the nation’s largest concrete gravity dam and harnesses the mighty power of the Clutha River. The powerhouse is capable of generating 432 megawatts of electricity, which is close to the consumption of Christchurch and Dunedin combined. The operating range of Lake Dunstan varies between 193.5 and 194.5 metres above sea level.
The lake consists of three arms, the Kawarau Arm (2.27 sq. km), the Clutha Arm (14.78 sq.km) and the Dunstan Arm (7.96 sq. km.). The Clutha Arm ﬂooded productive farmland for fifteen kilometres
upstream of Cromwell and its shallow waters have the greatest value as a fisheries resource.
The Kawarau Arm and the Dunstan Arms have steeper sides and consequently much smaller productive littoral areas than the Clutha Arm. In addition, these two arms are affected to a greater extent by a high sediment inflow which originates in the Shotover River, a tributary of the Kawarau River.
Lake Dunstan contains brown trout, rainbow trout, quinnat salmon (landlocked), redﬁn perch
long finned eel, probably two species of Gobiomorphus (bullies) and possibly two species of Galaxias (whitebait).
Initially, the fishery followed the same path as elsewhere when fertile land is covered in water. The concentrated nutrients have had a dramatic effect on the food chain, from the basic phytoplankton and zooplankton, through the aquatic invertebrates and on to trout and other fish. The huge amount of trout food resulted in impressive growth rates and high condition factors for both rainbow trout and brown trout.
Immediately after lake-fill was completed, earthworms were one of the main forms of trout food, but as they ran out, Chironomid midges became the most important food source. The larvae, known as bloodworms, live in the bed of the lake, feeding on detritus and other organic matter. When they pupate, they become available as trout food. Chironomids are very quick to become established because of their short life cycle, which under optimum conditions can be completed in as little as twelve days. During the summer of 1992/93, millions of empty pupal shucks from the hatched midges could be seen ﬂoating in rafts on the lake. Indeed at that time, Lake Dunstan was a Chironomid-based fishery.
On 7/8 January 1994, a natural disaster involving massive ﬂoods hit the lower portion of the South Island. Heavy silt loads flowed down the Clutha River and much of this settled on the bed of the Clutha Arm of Lake Dunstan. The fine silt dramatically reduced water clarity and covered the rotting vegetation, effectively killing off the Chironomid populations. The large water snail Lymnaea stagnalis also perished. As a result of the ﬂood, both rainbow trout and brown trout were unable to find food and their condition became very poor. The water cleared over the next few months, but the Chironomids were all but absent from the aquatic invertebrate fauna. The rainbow trout turned to a diet of small water snails, however, the brown trout initially appeared to be unable to take an advantage of this food source. The lake had undergone a change in its biological structure, from a Chironomid based
fishery to one based on molluscs.
It was only more recently that the Lake Dunstan fishery started to recover from the effects of the January
ﬂood. At the head of the Clutha Arm, the noxious aquatic plant Lagarosiphen is becoming well established. These dense weed beds are ideal habitat for molluscs such as water snails, and both
rainbow trout and brown trout are now taking advantage of this important food resource. Also taken as food by trout are damselfly nymphs, backswimmers, water beetles, caddis nymphs and to a lesser degree, Chironomids.
The Environmental Impact Report on Design and Construction Proposals – Clutha Development (December 1977), correctly identiﬁed that ﬁsh and wildlife represented the two most important recreation and conservation resources within the area affected by Lake Dunstan.
Condition 15 of the Clutha Development (Clyde Dam) Empowering Act 1982 required the Minister of Energy (as a condition to the granting of a water right), to provide a ﬁsh hatchery for the purposes of re-establishing and maintaining stocks of sports ﬁsh in Lake Dunstan and the reach of the Clutha River below the Clyde Dam.
It was decided by ﬁsheries management authorities and ECNZ that this condition was too restrictive, particularly if research showed that a trout hatchery was not required. Some managers were of the opinion that recruitment from the existing wild ﬁsheries would naturally stock Lake Dunstan. It was agreed to by all parties involved that the best way for ECNZ to discharge its obligation under Condition 15 was to form and fund a ﬁsheries trust, and apply for a variation so that a hatchery was only required to be built if it was deemed necessary through research funded by the trust.
The ECNZ Clutha Sports Fisheries Trust was formed and ﬁve Trustees were nominated by those bodies who had an interest in the Lake Dunstan ﬁshery. The Trustees were: Dr Bob McDowall (National Institute of Water and Atmospheric Research Ltd.), Murray Neilson (Department of Conservation), Dr Donald Scott (New Zealand Fish and Game Council) and John Barlow and Dick Marquand (Otago Fish
and Game Council).
On 4 August 1992, ECNZ presented the Trustees with a cheque made out for $2.7 million. This money has been invested and the interest is paying for research that will enable a decision to be made on whether or not a hatchery is required. If the research shows a hatchery is required, one will be built, if the research shows otherwise, the funds will be used to undertake fisheries management programmes,
such as enhancing spawning streams so that spawning and natural recruitment can help sustain the ﬁshery.
A number of research programmes are presently being funded by the Trust. Between 1992 and 1994, 50,000 tagged rainbow trout fingerlings were liberated in Lake Dunstan and the associated waterways. These trout were reared at the Wanaka Trout Hatchery under the control of the Otago Fish and Game Council, the statutory authority responsible for sports fisheries management in Lake Dunstan. Each fingerling has had a minute micro-coded stainless steel wire tag implanted in its nose cartilage. The adipose fin has also been clipped for ease of identiﬁcation when caught by anglers.
The second research programme requires the sampling of wild trout and salmon from Lake Dunstan and the Clutha River. It involves the collection of stomach samples for sports ﬁsh diet studies, and the collection of scales, ﬁns and otoliths (ear bones) for age and growth studies.
The third research programme being funded by the Trust is the collection of data relating to angling effort and success, as well as information on the anglers who are using this resource. Since December 1992, a staff member of the Otago Fish and Game Council has been undertaking ﬁsheries surveys four
times a month on Lake Dunstan. These have shown that the average angler spends about four hours fishing for each trout landed.
It is well known that 10 percent of the anglers catch 90 percent of the fish and this is very evident on Lake Dunstan. The following information will hopefully put you into the successful 10 percent bracket.
The four species of sports fish found in Lake Dunstan are brown trout, rainbow trout, quinnat salmon and redfin perch.
Brown trout are found in the lake all year round and can weigh in excess of 4kg. The biggest I have seen caught weighed 5.7kg. This was caught and released by myself in the Clutha Arm during November 1992. Brown trout are plentiful around the shallow margins of the lake, particularly at the head of the Clutha Arm, within the Bendigo Wildlife Management Reserve. Anglers are well advised to remember that brown trout tend to patrol a “beat,” particularly around the margin of the lake. Brown trout are autumn and early winter spawners. Bendigo’s historic and scenic reserves and associated conservation areas are well worth visiting for their historic and natural features.
Rainbow trout are also found in the lake all year round and can weigh in excess of 3.5kg. The heaviest I have seen was a jack which weighed 6.5kg, poached from the Bannockburn Stream in October 1993.
When hooked on light tackle, rainbows provide spectacular sport. They are found throughout the lake but again tend to prefer the productive upper Clutha Arm. Rainbow trout do not tend to patrol a “beat.”
Quinnat salmon are particularly common in Lake Dunstan from the third week in October until after Christmas, when they migrate downstream from Lakes Wakatipu, Wanaka and Hawea. A large landlocked quinnat salmon from the upper Clutha catchment would weigh around 0.95kg; claims of larger salmon invariably turn out to be either rainbow trout or brown trout. Quinnat salmon tend to move about in schools, they are easy to target and easy to catch. They are found in all three arms of Lake Dunstan and are targeted by Clyde and Alexandra anglers in the lower end of the Dunstan Arm, close to the dam.
Prior to Lake Dunstan, redfin perch inhabited the dredge holes upstream of Cromwell as well as the backwaters of the Clutha River. They are now found in all three arms of the lake, being a particularly common catch by worm anglers who ﬁsh the Lowburn Inlet and the Bannockburn Inlet during summer. This species is expected to take advantage of the Lagarosiphon weed beds for spawning and feeding, in
the shallow waters of the upper Clutha Arm. Redﬁn perch are rarely seen in the winter months, however, during summer, schools containing some hundreds of individuals can be seen cruising the margins of the Clutha Arm. A large redfin perch would weigh in excess of 0.8kg.
Fishing Methods for Lake Dunstan
Four methods of angling are undertaken in Lake Dunstan, these being fly fishing, threadline fishing (spinning), trolling and worm fishing.
Fly ﬁshing is a very productive method of catching trout on Lake Dunstan, particularly during the warmer months. Again, the most productive area for ﬂy ﬁshing is in the Clutha Arm, especially within the Bendigo Wildlife Management-Reserve.
Both brown trout and rainbow trout can be taken while blind ﬁshing the margins of the lake using a sinking fly line and a Woolly Bugger or a killer pattern such as a Mrs Simpson and a Hamill’s Killer. The fly is cast, allowed to sink and retrieved in a series of short sharp jerks. These same ﬂies work well when the “ambush method” is used on a cruising trout. I ﬁsh with a ﬂoating line and cast well ahead of a trout cruising the shallow edge, allowing the ﬂy to sink to the bottom. When the trout is within visual range of the ﬂy, a couple of short sharp jerks will usually induce a strike. This same method works well with dragonfly nymph imitations such as the McDonald Mudeye, Morton’s Annie, and so on, although it must be remembered that populations of dragonﬂy nymphs will take some years to become properly established in Lake Dunstan. However, these nymphs were present in the many dredge ponds that became inundated and so I am sure a drazonﬂy nymph ﬁshed correctly will almost certainly produce the required result.
Damselﬂy nymphs are particularly deadly on both rainbow trout and brown trout at the head of the Clutha Arm, fished singly or as a dropper under a dry ﬂy. Many Lake Dunstan trout have fallen victim to Pete Lemin’s version of this nymph.
Water boatmen/backswimmer imitations are another very successful fly when fished on a ﬂoating ﬂy line in the shallow water to trout that have been spotted. The ﬂy is retrieved in a series of very short jerks. This is a particularly deadly fly in the shallow waters of the Bendigo Wildlife Management Reserve. I have watched trout almost strand themselves while feeding on backswimmers.
The Snail Fly is yet another deadly pattern, particularly in the Clutha Arm where molluscs now form the majority of the trout’ s diet. Again, the Snail Fly is ﬁshed on a ﬂoating ﬂy line and is most deadly when the “ambush method” is used.
Midge populations will never be as they were prior to the great ﬂood of January this year, however, pockets will re-establish, particularly at the head of the Clutha Arm.
Fishing the midge pupa is a specialised form of angling. The method I have found to be most successful is by using a ﬂoating ﬂy line and greasing or putting fly ﬂoatant on all but the last 30 to 50 centimetres of tippet. It is important not to allow the ﬂoatant to get on the artiﬁcial as it must not ﬂoat on the surface. The natural position for a Chironomid pupa is to be suspended vertically. If you think this is not important, then realise that you will be presenting your artificial amongst dozens of naturals and hoping for a take from a selective trout. A short draw on the line will give the artificial movement that will be quickly spotted by a hungry trout.
From experience, I have found the best time to take trout on an artificial midge pupa is during the evening when trout can often be seen bulging as they take naturals. Midge pupa in shades of dark brown appears to work best for Lake Dunstan.
During the warm evenings of late spring and early summer, the grass grub beetle takes to wing. The cumbersome ﬂight of this plump insect often ends up with a wet landing and trout feast upon these tasty morsels. The Brown Beetle dry or a large Coch-y-bondhu will produce the required results. These beetles crash land with quite a splash so a delicate presentation is not necessary.
The Deer Hair Sedge is another ﬂy well worth using on Lake Dunstan. These are of course fished with a ﬂoating ﬂy line during the late evening and at night. Various terrestrials such as the Black Gnat, Brown Bee, and so on, will also take trout from this water during the summer and autumn months.
If you decide to fish the Bendigo Wildlife Management Reserve during the Christmas holiday period, a few Willow Grub artiﬁcials will not go astray. The galls on the crack willow leaves are an indication of the high expectations I have for this pattern.
Threadline or Spin Fishing
The threadline angler is again best to concentrate his or her efforts in the Clutha Arm of Lake Dunstan, particularly towards the head. The traditional angler will catch both rainbow trout and brown trout on the Black Toby, Black Wedge, Veltic and the darker Jensen Insect and Mepps spinners. However, the angler who really wants to catch trout should consider using minnows such as the Rapalas, RTB Legend Minnows, Tilsans and Rat-L-Traps, particularly the ﬂoating models.
Floating minnows can be retrieved up to an obstruction such as a log, weed beds and so on, then allowed to ﬂoat over the snag before being cranked back down to the strike zone. The best areas to target are those close to weed beds, as this is where the trout will be found to be feeding.
Some of the ﬁnest sport I have had on Lake Dunstan has been while threadlining with small minnows such as the Rapala CD 5s, RTB Legend Minnows and Tilsans from a drifting boat. It is great watching large trout racing the minnow back to the boat and when hookups occur, they are spectacular. A drifting boat offers an opportunity to ﬁsh some very productive water and will guarantee success.
Top patterns appear to be bright colourful lures on dull days and dull lures on bright days. This has certainly been my experience on Lake Dunstan since filling commenced in 1992.
Those lures with built-in rattles such as the RTB Legends, Rat-L-Traps and Rattlin’ Rapalas give off a sonic attractant and work particularly well when the Clutha Arm becomes discoloured by heavy rainfall in the adjacent mountains.
The secret of successful threadlining is a light but powerful rod capable of casting lures in the 4-gram to 8-gram range, a good reel with a very smooth drag system, good quality line in the 2kg to the 2.7kg range and proven lures that you feel conﬁdent ﬁshing with. The minnows that I have previously mentioned can be used with confidence.
Lake Dunstan is popular as a trolling water. When the sky is clear and blue, with not a breath of wind, I often hear the comment “it would be a great day fishing.” Such days may be pleasant for boaties, but they usually are not very productive days for trolling. The best days to troll for trout are when the lake is described as being moderate to rough. Often a sudden change of wind direction can bring the trout on to take lures ravenously, or it can kill the action completely.
Before the great ﬂood of 1994, trout were more or less evenly distributed in the upper portion of the Clutha Arm. Trout food such as Chironomids must have been found over huge areas of the lake bed.
Following the ﬂood, I found areas that previously supported good fishing, appeared to be dead. I believe the reason for this is that the vast areas of ﬂooded farmland which contained rotting vegetation became covered in a thick layer of inorganic silt. The trout now appear to be more concentrated in smaller areas.
One of the most important pieces of equipment for trolling on Lake Dunstan is a quality depth sounder/ ﬁsh ﬁnder. This will enable the angler to ﬁnd ﬁsh and determine whether they are all close to the bottom, or evenly distributed through the water column.
The next step is getting your line down to them. The depth of water you intend trolling maybe two metres deep or it may be in excess of ten metres. For trolling the really shallow water at the head of the Clutha Arm, I use a standard threadline rod, reel and line. For water varying in depth from three to six metres, I use a trolling rod with a free spool reel that has backing attached to ten or ﬁfteen metres of leadline. Such a setup allows you to get your lure down and a lot further behind the boat than if you were using a standard full length of leadline.
Sometimes you want your lure well out. For water from six to ten metres in depth, I use an identical outﬁt with thirty or forty metres of leadline attached. I only use a standard leadline for ﬁshing really deep water. It is important to have a leader of around ten metres between the end of the leadline and your lure.
The setups I have described work well with standard lures, but not deep diving minnows. These lures have a large bib that acts as a paravane diving the lure deep behind the boat. Some experience is needed when using such gear otherwise your expensive deep diving minnow will surely foul the bottom. With a standard monoﬁlament line, a deep diving minnow can go as deep as four or more metres when only ten metres from the stern of the boat. Minnows are both expensive and productive, so if you are not experienced in their use and habits, I would advise you to use shallow running models.
Right, onto trolling lures for Lake Dunstan. To be in the 10 percent that catches 90 percent of the ﬁsh, you need to know not only what lures to use, but also the preferred colours for different situations.
These all work well in Lake Dunstan. As space here is limited, I will comment only on the King Cobra range.
When the water is clear, the most productive model is the No. 63 (red, yellow and green traffic lights” pattern). The No. 75 (gold with a red stripe) is another very good pattern for these conditions.
In the shallow water over the weed beds at the head of the Clutha Ann, I prefer to use the No. 52 (green and yellow “harlequin frog.”) When the water becomes discoloured after heavy rain, the best two King Cobras are the No. 58 (ﬂuoro pink) and the No. 80 (red head with a ﬂuoro yellow/ green body). These ﬁve King Cobras are all proven colours that have a well-deserved place in the Lake Dunstan trolling angler’s tackle box. I prefer to use King Cobras because I feel that the jewel eyes are an important feature for attracting and encouraging trout to strike. Other brands, such as the ones I have already mentioned in similar colours will also catch Dunstan trout.
This type of lure can be made even more effective by replacing the standard internal wire and hook with a Kiwi Teaser, and ﬁshing this on a running rig. The Kiwi Teaser gives the lure a ﬂashy tail and increases strikes and hookups dramatically.
Rapala minnows such as the CD 5 and CD 7 models in the rainbow trout pattern are very successful lures for clear water conditions. If the water is a little murky, try the fire tiger, chartreuse and fluoro red/ gold patterns.
In recent years, we have seen a few sonic rattling lures come onto the New Zealand market. Believe me, these lures are about to take New Zealand by storm. We now have Rattlin’ Rapalas, RTB Legends, and by the time this article goes to print, there will be a very deadly “rattler” on the market, known as the Rat-L-Trap.
These lures contain sonic rattling chambers within their plastic bodies and when drawn through the water, the rattle becomes a fish attracting noise similar to an electronic hum. They are exceptionally deadly in both clear water and murky water situations.
My own experience shows that the rainbow trout pattern and the luminescent Glow Trap are the most productive, with very impressive catch rates when being trolled.
It is only right I should make mention of harling, or trolling Taupo type streamer ﬂies. Some anglers harl ﬂies using a ﬂy rod with a sinking fly line, or perhaps a short length of leadline tied to a backing, while others use a trolling rod with a free spool reel containing leadline.
Harling is a very effective method of catching fish in Lake Dunstan, particularly when the water is clear. The best flies for harling appear to be the plain old Red or Yellow Rabbit, but then everyone has their favourite. Pete Lemin won the 1st Annual Kilwell Sports – Lake Dunstan Fishing Classic in October 1993 with a trout he caught while harling one of his home tied rabbit ﬂies. As Pete will tell you, the main points are to troll at a slow boat speed and work the ﬂy by drawing and releasing the line with your spare hand.
Worm fishing has its following, particularly by elderly and young anglers. In this neck of the woods, most youngsters start out on their trout ﬁshing careers by worm ﬁshing. Some big catches of trout are made by worm anglers, particularly when a margin of the lake becomes murky due to an onshore wind. Again, the Clutha Arm is the most productive area for worm ﬁshing.
Although the vast majority of worm anglers ﬁsh a worm on the bottom, a few prefer to fish the worm under a small plastic bubble. This results in less lost gear from snags.
I recently watched a 10-year-old girl do battle with a big jack brownie that had taken a worm. Rachael Gardyne landed the magniﬁcent trout which weighed in at 4.25kg.
The Bendigo Wildlife Management Reserve lies at the head of the Clutha Arm. This area is managed by the Otago Fish and Game Council for its wildlife and ﬁsheries values. It is a trout fishing paradise, particularly for fly anglers. Access to the eastern side of the reserve is from the Rocky Point picnic area.
Access to the western side is from the Cromwell-Wanaka highway through the gate marked 24A. Boat traffic is requested to use the buoyed high-speed access lane when passing through the reserve and to keep boat speed at less than 5 knots in other parts of the reserve. This will help to avoid unnecessary disturbance of wildlife and anglers.
There is road access to the majority of Lake Dunstan. The Dunstan Arm has access along the length of its northern shoreline from the Cromwell-Alexandra highway. There are three boat launching ramps, one on each side of the lake near the Clyde Dam and one at Champagne Gully. Access to the eastern side of the Clutha Arm is from the Cromwell-Omarama highway.
There is some access from the Cromwell-Wanaka highway, however, access to the upper section of the western shoreline is as is shown in the access guide booklet published by the Upper Clutha Angling Club.
The four boat launching ramps on the Clutha Arm are at Bendigo and Northburn on the eastern side, and at Lowburn and McNulty Inlet on the western side. The Kawarau Arm is of very limited value to anglers, however, there is a boat launching ramp in the Bannockburn Inlet and two below the old Cromwell Township.
The information contained within this article is the result of my previous work with the New Zealand Wildlife Service and Department of Conservation when I was employed as a Fish and Game Officer, my work undertaking ﬁsheries surveys on Lake Dunstan for the Otago Fish and Game Council, the countless hours I have spent on the lake testing ﬂies and lures, and when trout guiding, and my work with the Electricorp Production Clutha Sports Fisheries Trust. The lures and methods I have explained work for me – I hope they work for you
Otago Fish & Game Council Lake Dunstan pamphlet .pdf (scroll down the page).