This is what NZfishing.com has to say
The Halswell River meanders from near the Halswell township down to Lake Ellesmere. It crosses many public and private properties and flows beneath several bridges. Access to the mouth can be had from where the river intersects with Seabridge Road down either bank just south of Motukarara.”
and the trout bible ” South Island Fishing guide” by John Kent.
“the mouth offers night lure fishing, while the middle reaches hold a few small brown trout……….. “
I know its off topic, but if you do not already own a copy “South Island Fishing Guide” is essential to own for any keen trout fisherman. It gives a brief overview of most rivers and is accurate enough to be useful.