Ninth Circuit clarifies Clean Water Act irrigated return flows exemption

The U.S. Court of Appeals for the Ninth Circuit ruled that drainage conveyed through the Grassland Bypass Project into the San Luis Drain qualifies for the Clean Water Act’s irrigated return flows exemption (Pacific Coast Federation of Fishermen’s Associations v. Nickels, No. 23-15599). The decision confirms that discharges “composed entirely of return flows from irrigated agriculture” under 33 U.S.C. § 1342(l)(1) can include commingled nonpoint source pollutants and point source discharges tied to crop production, but the exemption does not apply if additional point source discharges are unrelated to agriculture. 

The court found the term “entirely” in the statute ambiguous and interpreted it to exclude only added point sources unrelated to crop production. It emphasized that Congress intended the exemption to reduce permitting burdens, ensure fairness between rain‑fed and irrigated farming, and address tracing challenges.

The ruling also noted that some nonpoint pollutants, such as windblown dust, will inevitably mix with return flows. Applying this interpretation, the court determined the four pollutant sources at issue were either nonpoint in nature or point sources related to crop production, leaving the Grassland Bypass Project outside NPDES permitting requirements.