## Facts

- The Los Angeles County Flood Control District operated a municipal separate storm sewer system (MS4) consisting of channels and pipelines that conveyed stormwater to navigable waters.
- The District held an NPDES permit regulating discharges in multiple watersheds, including the Los Angeles River and the San Gabriel River.
- Environmental groups sued under the Clean Water Act (CWA), alleging that monitoring stations within concrete-lined portions of the rivers recorded pollutant levels exceeding permit limits.
- The theory relevant on review treated the flow of polluted water from the concrete-lined segments through District-operated conveyances into downstream, unlined segments of the same rivers as a CWA “discharge of a pollutant.”

## Issues

1. Whether the flow of polluted water from a concrete-lined segment of a river to an unlined segment of the same river constitutes a “discharge of a pollutant” under the CWA.

## Decision

- The Supreme Court unanimously reversed the Ninth Circuit and remanded.
- The Court held that the flow of water from an improved portion of a navigable waterway into an unimproved portion of the same waterway is not a “discharge of a pollutant” under the CWA.
- The Court limited its decision to the question presented and did not resolve broader disputes about permit interpretation or other potential bases for liability.
- Justice Alito concurred in the judgment.

## Legal Principles

- A CWA “discharge of a pollutant” requires an “addition” of pollutants to navigable waters from a point source.
- The movement of polluted water within a single, continuous water body does not constitute an “addition,” even if the water passes through engineered channels.
- Treating different segments of the same river as distinct receiving waters for purposes of finding an “addition” is inconsistent with the statutory “addition” requirement as applied to transfers within the same water body.
- A conveyance that merely transports water within the same river, without adding pollutants to it, does not by that fact alone create discharge liability under the “addition” element.

## Conclusion

The Court rejected a theory of Clean Water Act liability based solely on the transfer of already-polluted water from a concrete-lined reach of a river to a natural reach of the same river, holding that such intra-river movement is not an “addition” of pollutants and therefore is not a “discharge of a pollutant” requiring NPDES permit liability on that ground.


Los Angeles County Flood Control Dist. v. Nat. Res. Def. Council, Inc., 568 U.S. 78 (2013)