Researchers have observed clear, biologically diverse streams transformed into muddy streams with thousands of crayfish. Crayfish first devour the vegetation that stabilizes stream banks and bottoms, before eating the pond snails, the mayfly larvae, caddisfly larvae and other insects. Their menu then expands to include tadpoles, fish, turtles and even garter snakes.
Trout can eat small crayfish.
Larger crayfish, however, go unchecked and eat the fishes' food supplies. Arizona Game and Fish is in the process of adopting a law to make it illegal to transport crayfish live. Nevada and Utah already have a similar law, and California and Montana may soon follow suit. Arizona is the only mainland state with no native species of crayfish. Their introduction to the state was partly due to government agencies releasing the critters into state waters to control weeds and feed bass and other game fish.