From DCYC’s Naturalist, John Lusk, on the flies: You’ve seen them. Here is what they are.

• Common names include:  lake flies, bay flies, sand flies, muckleheads,  muffleheads, Canadian soldiers, American soldiers, blind mosquitoes, and chizzywinks.
• The are not mosquitoes
• Known as one of the indicator organisms
• Larvae and pupae serve as important food sources for fish

https://en.m.wikipedia.org/wiki/Chironomidae