Eating fish from Ellesmere is fine, otherwise the commercial operators would not be allowed to fish it. Many people even continue to eat flounders through the warnings… Despite the lakes poor health, it continues to hold very high numbers of Flounders. The water should even become a bit clearer when the lake gets open shortly , although likely to remain to dirty for spearing.
It is not unheard of to catch 50+ Flounders for every set of a net.
This video which was from April this year shows Set Netting in the lake, plus commentary on the illegal flounder poaching.
Would PM you a spot which should be worth a try.