S. D. Warren Co. v. Maine Board of Environmental Protection, 547 U.S. 370 (2006), was a case decided by the Supreme Court of the United States involving licensing requirements under the Clean Water Act.

The S. D. Warren Company operates several hydroelectric dams along the course of the Presumpscot River in southern Maine, which generate electricity for its paper mill.

The Maine agency issued certifications that required Warren to maintain a minimum stream flow in the bypassed portions of the river and to allow passage for various migratory fish and eels.

FERC eventually licensed the five dams subject to the Maine conditions, but the company continued to deny any need for state certification under section 401.

Though Chevron deference did not apply in this context, the Court nevertheless believed that those usages of "discharge" by those agencies "confirms our understanding of the everyday sense of the term."