The San Francisco Bay Area is the fourth largest metropolitan region in the United States. Its unique geographical setting and climate make it one of the most attractive places to live in the world. Part of its attraction comes from the beauty of its complex natural surface water system, which includes the Bay itself, its estuary, the Pacific Ocean, and numerous streams and rivers. The many beneficial uses of these surface waters include municipal and agricultural supply, industrial process supply, groundwater recharge, water recreation, wildlife habitat, shellfish culture, commercial and sport fishing, and habitat for multitudes of freshwater and marine organisms. Protection of these waters from pollutants is a high priority, because the intricate and delicate balance of this surface water system is critical to the entire ecosystem of the area.