A watershed scale study of fish passage in a roaded corridor has been completed in a drainage just north of Yellowstone National Park that holds tributaries to the Yellowstone river. The experiment relied heavily on the use of PIT tag technology, and resulted in statistical descriptions of fish progress through the natural stream reaches and the culverts and bridges that span the stream. The results of the project are summarized here along with a method for using this type of information to make large scale decisions concerning the order in which fish passage issues should be dealt with.