Are you still at 100%? this is a dragonfly larva. You can tell the difference basted on the dorsal parts of the thoracic segments (so the stoneflies tend to have more defined ones.) The dragonfly also has a bum that is extended for jet propulsion. Literally, hah. The most diagnostic is the mouth.
Literally like a spoon attached to an arm that sits like a darth vader mask when not extended. That is so diagnostic.
Check it out if you have the corpses still, it takes a second and will help us figure out your mystery more!
Edit:
THIS IS PURELY TO GET AN ID AS YOU ASKED FOR ONE. WHAT YOU HAVE WILL NOT AND CANNOT CAUSE ISSUES UNLESS YOU ARE HANDLING FRY OR VERY SMALL FISH.