In a ruling that has important implications for the hydropower industry, municipal water control systems, and dam owners everywhere, the U.S. Supreme Court strongly affirmed an earlier holding that a "discharge of a pollutant" as regulated by the Clean Water Act does not occur when polluted water flows from an improved, man-made portion of a navigable water way into an unimproved portion of the same waterway. 

When monitoring stations on the Los Angeles and San Gabriel Rivers indicated repeated exceedances of water quality standards in those water bodies, the Natural Resources Defense Council and the Santa Monica Baykeeper brought suit under the Clean Water Act ("CWA"), charging that the Los Angeles County Flood Control District (the "District") was in violation of its permit.  The District operates a municipal separate storm sewer system that discharges to the rivers.  Because the monitoring points are within concrete channels constructed for flood control purposes, the Ninth Circuit Court of Appeals had held that discharge from these concrete channels into the unimproved waterways below constituted a discharge under the CWA regulated by the District's discharge permit. 

The Supreme Court, in an opinion by Justice Ginsburg, held that "no discharge of pollutants occurs when water, rather than being removed and then returned to the water body, simply flows from one portion of the water body to another."  This holding follows closely the reasoning of the Court's 2004 decision in South Fla. Water Mgmt. Dist. v. Miccosukee Tribe, 541 U.S. 95, where the Court determined that pumping polluted water from one part of a water body into another part of the same body is not a discharge of pollutants under the CWA.  Justice Ginsburg drove home the point with an apt analogy from the Miccosukee opinion, that, "f one takes a ladle of soup from a pot, lifts it above the pot, and pours it back into the pot, one has not "added" soup or anything else to the pot."  Like a good soup, this opinion should bring some comfort to hydropower operators and dam owners.