This is a Fishfly. They look similar to Dobson Flies (because they are related), but their antennae are much larger and feathery, like that of a moth. Their mandibles are also much smaller, so they don't look nearly as fierce. Like Dobson Flies, Fishflies live in the water during their nymph stage, and only get their wings when they emerge as adults. They are a favorite food of many fish, and fly fishermen have been known to make some very convincing imitations to tempt hungry fish.