The purpose of this law is to make the waters of the United States safe for swimming and fishing.
At the time of its establishment, over 35% of the nations rivers are unsafe. Bacteria in the Hudson River is 170 times the safe limit.
The Clearwater is a recreation of the Sloops that used to sail the River in the late 1800's. It's purpose is to get people out on the river to mobilize opinion and action to protect the river.