The Cosumnes River is in the northern part of the study area and drains directly to the Sacramento-San Joaquin Delta. The Cosumnes is essentially the last significant free-flowing river from the Sierra Nevada, with only minor regulation by a small upstream reservoir. Past mining activities inthe Cosumnes river Basin occurred upstream but within the basin. The Cosumnes River is sampled upstream of most of the agricultural activity in the basin, and therefore is representative of a "reference" for unaffected water quality.

The Cosumnes River is being sampled for water-borne constituents and biological characteristics as part of the Trend Network for Streams. Water, fish and streambed sediment were also sampled for mercury and methylmercury in the summer of 2002 as part of the Status Assessment for Mercury.

Cosumnes River Basin


Cosumnes River
(Photograph by Jason May, U.S. Geological Survey)