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84 Part I California Water 2.2 How salty is it? Sierra runoff contains roughly 50 milligrams per liter(mg/I)of dissolved solids (0.005 percent salt by weight),the Sacramento River roughly 150 mg/I,the Colo- rado River(at the Nevada border)about 700 mg/I,and the middle reaches of the San Joaquin River about 775 mg/I(0.0775 percent salt by weight).Yields for many crops begin to steeply decline when irrigation water salinity exceeds about 950 mg/I,and urban water treatment and use become much more expensive with salt concentrations above 500 mg/I.Seawater has 33,000 mg/I of salts(3.3 percent salt by weight).Salton Sea and Mono Lake—two"terminal"inland lakes in Califor- nia that do not flow out to the sea—have salinity levels of roughly 44,000 mg/I and 81,000 mg/I,respectively.(Dead Sea salinity is about 220,000 mg/I(22 percent salt by weight);Utah's Great Salt Lake salinity varies between 50,000 and 270,000 mg/I depending on lake levels.) has reduced agricultural production,deprived local cities such as Stockton and Lathrop of a water source,and compromised habitat for native fish species.In western areas of the San Joaquin and Tulare Basins,salt accumulations in soils and groundwater have reduced output and removed some land from produc- tion, with more land threatened as salts continue to accumulate (Chapter 3). Increasing salinity is diminishing the recreational and environmental uses of the Salton Sea—a man-made inland sea fed by drainage water with no outflow to the ocean and little natural inflow,which is already almost 50 percent more saline than seawater(Box 5.4). Many other,more localized,water quality problems exist as well(Figure 2.7). The accumulation of excess nutrients including nitrogen and phosphorus often leads to a proliferation of plant life, especially algal blooms, in lakes and sec- tions of streams. Sediment as well as algae growth from nutrients can reduce the clarity of lakes, as with Lake Tahoe. And by-products of fertilizers and pesticides can accumulate in aquifers and streams. In many rural areas, the accumulation of nitrates in groundwater has become a serious concern and a problem for local drinking water users. As a result of groundwater overdraft, some coastal aquifers(e.g.,the Salinas and Pajaro Basins in the Central Coast) suffer from seawater intrusion. California must also contend with the legacies of toxic chemicals introduced by mining activities long ago, such as mercury (Chapter 3).