CWA Irrigation Return Flow Exemption

Irrigation Return Flow Exemption

The U.S. Supreme Court declined to review a Ninth Circuit ruling that preserved the Clean Water Act’s permit exemption for irrigation return flows. The dispute centered on California’s Grassland Bypass Project. The Project conveys farm drainage from about 97,000 acres in the San Joaquin Valley into the San Luis Drain. From there it goes to a slough that empties into the San Joaquin River.

The river is a protected water under the CWA.

The Project has operated without a permit since 1997 under the statute’s irrigation return flow exemption.

Environmental groups filed a law suit in 2011. They asserted that the exemption shouldn’t apply because the drainage water, while being transported, commingled with pollutants from nonagricultural sources before reaching protected waters. In a 2025 decision, the Ninth Circuit held that the presence of nonpoint source pollution does not negate the exemption unless there is a separate point source discharge unrelated to crop production. The plaintiffs sought Supreme Court review. The Court’s refusal to hear the case leaves the Ninth Circuit’s decision in place