While out swimming yesterday, I noticed a few of these little snails sitting on a rock beneath the water line. Having never seen any before, I picked a few up, took a picture, and asked Emily DeBolt of the Lake George Association what they were. Here is part of her response to me:
They look like banded mystery snails. They are actually non-native to the lake – but have been here for at least 100 years – probably longer – so they are pretty well established. Their impacts are not well known – so they aren’t considered ‘invasive’ per se – just ‘ non-native’ at this point. But that point could be debated by experts in the field…. They are usually just in the sand – not on rocks – but they could have been on a rock as you said. These things have ‘boom and bust’ cycles for reasons that we don’t necessarily understand – and I would say that this looks like this year we had a ‘bust’! Snails are associated with swimmer itch – along with ducks and geese. The ‘itch’ is actually traveling between the snails and the waterfowl when the ‘swimmer’ accidentally gets in the way.
So now you know.