The NRDC and Baykeeper urge that the Court of Appeals reached the right result, albeit for the wrong reason. The monitoring system proposed by the District and written into its permit showed numerous instances in which water-quality standards were exceeded. Under the permit's terms, the NRDC and Baykeeper maintain, the exceedances detected at the instream monitoring stations are by themselves sufficient to establish the District's liability under the CWA for its upstream discharges. This argument failed below. It is not embraced within, or even touched by, the narrow question on which we granted certiorari. We therefore do not address, and indicate no opinion on, the issue the NRDC and Baykeeper seek to substitute for the question we took up for review.

JURIST Guest Columnist Roderick Walston recently considered the case [JURIST comment]. "The Ninth Circuit's reasoning is troubling. Since the CWA prohibits the 'discharge' of pollutants into waterways from a 'point source,' the location of the point source that is the original source of the pollution is vital in determining the applicability of the CWA and whether a discharger has violated it. The CWA prohibits only the original discharge of pollutants into the waterways from a point source, and it does not prohibit another discharge of the same pollutants in the same waterway. As the Court held in an earlier case [opinion], there has been no 'addition' of a pollutant to 'the waters of the US' within the meaning of the CWA unless the waters from which a pollutant has been conveyed are 'meaningfully distinct.' Since the character of the Los Angeles and San Gabriel rivers are not different above and below the monitoring stations and the downstream outfalls, these segments of the river are not 'meaningfully distinct' within the meaning of the Court's decision in Miccosukee Tribe, and there has been no 'addition; of a pollutant to 'the waters of the US' simply because the pollutants passed through these facilities.'"