It's mosquito or black fly larva found on the rocks near the rapids. They are harmless. Be safe and shower after you are done swimming. Make sure all open wounds are properly covered.
I have been there about 4 or 5 times never seen them in that part of the river but have seen them in other places. I thought they are leeches of some kind but ain't sure.
We never had or seen any worms.
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