San Joaquin River Water Quality as a Limiting Factor for Salmonid Reintroduction

The restoration goal of the San Joaquin River Restoration Program is to restore and maintain fish populations in "good condition" in the main stem of the San Joaquin River below Friant Dam (near Fresno, CA) to the confluence of the Merced River, including naturally reproducing and self-sustaining populations of salmon and other fish. The San Joaquin River has a long history of water quality issues, a result of both agriculture land uses and urban development. The presence of contaminants, including organophosphates, carbamates, selenium, copper, and mercury, is well documented on the San Joaquin River and its tributaries, and biological effects have been associated with such contaminants.  These contaminants and others pose potential problems for restored populations of salmonids and other native fishes. Sub-lethal effects of pesticides are also a concern for aquatic organisms in the San Joaquin River.  Sub-lethal concentrations of contaminates can negatively affect growth, swimming behavior, reproduction, and immune-system response in fish and aquatic invertebrates. Water-quality monitoring has been ongoing since the early 1990’s, and this program has detected some contaminants, such as copper, at concentrations known to cause sub-lethal effects in fishes.  Results of a review of past and current studies of water-quality issues in the San Joaquin River and its tributaries suggest that current monitoring should be maintained and improvements to the monitoring program be considered so that the effects of contaminants on restoration efforts can be fully evaluated as the program proceeds.