The McCarran Amendment and Groundwater: Why Washington State Should Require Inclusion of Groundwater in General Stream Adjudications Involving Federal Reserved Water Rights

All water is connected through the hydrologic cycle. When a farmer pumps water from an underground aquifer to irrigate crops, that act may affect a family relying on a nearby surface water stream for its water supply. Despite the scientific link between surface and groundwater, the law often treats the two separately. The legal choice to ignore the interaction of surface and groundwater is particularly notable in “general stream adjudications.” States file these large-scale lawsuits against users in a particular stream or waterbody to determine, in a single lawsuit, all the rights existing in that water source. In 1952, Congress passed the McCarran Amendment, which allows states to adjudicate federal reserved water rights in state court in general stream adjudications. The United States Supreme Court has interpreted the Amendment as requiring that adjudications be “comprehensive” of all of the rights in a given water source, but has not yet ruled as to whether this requires inclusion of groundwater users. The Amendment itself is equally vague on this point. This Comment argues against Ninth Circuit precedent and asserts that for a general stream adjudication to be “comprehensive” under the McCarran Amendment, it must include users of hydrologically connected surface and groundwate