Maybe you get confused by those news stories about fish swimming back into their native rivers from the ocean.
Put aside how they find their way... how do we, as humans, keep track of which species belongs where? How do species differ from stream to stream?
These are among the questions to be answered by an Aquatic Environmental DNA Atlas for the Western United States now in the works.
Dan Isaak of the Forest Service is one of the people helping to compile the atlas.
He visits with details about this massive project.