Selected water-quality data for the San Joaquin River and its tributaries, California, June to September 1985

Streamflow, specific conductance, and concentrations of dissolved solids, boron, molybdenum, and selenium were measured at 11 sites on the San Joaquin River and its tributaries approximately twice per month during June to September 1985. Streamflows were lowest in the San Joaquin River near Stevinson (median 43 cu ft sq /sec) and in Mud Slough (median 74.7 cu ft sq). The flow of the San Joaquin River increased downstream to Vernalis (median 2,460 cu ft sq); most flows are from the Merced (median 221.5 cu ft sq), Tuolumne (median 201 cu ft sq), and Stanislaus (median 1,390 cu ft sq) Rivers, which enter the San Joaquin River from the east. The Stanislaus River had the lowest median concentrations of dissolved solids (59 milligrams per liter), dissolved boron (10 micrograms per liter), and dissolved molybdenum (less than 1 microgram per liter). Dissolved selenium was lowest in the Stanislaus, Tuolumne, and Merced Rivers, and the San Joaquin River near Stevinson, all of which had concentrations that were not detectable at the level of 1 microgram per liter, except for one detection of dissolved selenium of 1 microgram per liter in the Tuolumne River. Mud Slough had the highest median concentrations of dissolved solids (1,425 milligrams per liter), dissolved boron (2,850 micrograms per liter), and dissolved selenium (21 micrograms per liter). The highest dissolved molybdenum concentrations were in Mud Slough (8 micrograms per liter) and the San Joaquin River at Freemont Ford (8 micrograms per liter). (USGS)