Water Quality and Water Quantity

Watershed management focuses mostly on water quality issues, but water quantity is extremely important in its own right. Writing for the U.S. Supreme Court in the case Jefferson City Public Utility District v. Ecology Dept. of Washington, Justice Sandra Day O'Connor said that the separation of water quality from water quantity (or flow) was an artificial distinction that had no place in a law intended to give broad protection to the physical and biological integrity of water. Further, she claimed that reducing water quantity or flow was capable of destroying all designated uses for a given body of water, and that the Clean Water Act's definition of pollution was broad enough to encompass the effects of reduced water flow. This Supreme Court decision upheld the State of Washington's right to require a minimum water flow necessary to protect salmon and steelhead and to disapprove a hydroelectric plant application that would have diminished the existing flow.

The amount of flow in rivers affects many issues of water quality and quantity together for example, pollutant concentration, water temperature, aquatic habitat, and recreational uses all of which prompts us to ask the crucial management question, "How much water does a river need?"