1 of Jefferson County v. Washington Department of Ecology, 511 U.S. 700 (1994), is a case decided by the United States Supreme Court that interpreted section 401 of the Clean Water Act.

The case involved an application by the Jefferson County Public Utility District and Tacoma City Light in northwestern Washington to build a hydropower facility on the Dosewallips River, first proposed in 1982 and known as the "Elkhorn Dam" project.

Environmentalist groups argued that the FERC was insensitive to recreation and protection of salmon and steelhead and asked the state to enforce its minimum flow standards.

[6] The Jefferson County PUD had looked to damming the Dosewallips River to provide hydroelectricity as well as drinking water to support long-term population growth.

[6][9] At a second hearing, the PCHB considered an argument from Tacoma and Jefferson alleging that the Department of Ecology had exceeded its authority in imposing the in-stream flows requirement to enhance the fishery, rather than maintain and preserve it.