Dredging About 7 million cubic yards of sediment are dredged from the Estuary each year, most of which is then taken to one of three aquatic disposal sites. Dredging activities may make pollutants deposited earlier in the Estuary newly available to biota. As the San Joaquin and Sacramento Rivers flow from the Central Valley into the Estuary, they bring along large amounts of pollutants. The rivers act as conveyances of pollutants that originate from both point and nonpoint sources along their banks. Fate of Pollutants Pollutants enter the Estuary in different chemical forms, change forms within the ecosystem, and move throughout the system in response to tides, freshwater inflows, and winds.
Many pollutants bind to particles of sand and silt.
Shrimp, clams, fish and other estuarine organisms can accumulate pollutants both directly from the water or from the ingestion of contaminated food. The feeding habits, physiology and habitat of each organism determines the degree to which it absorbs and tolerates pollutants. Whereas many organisms can adjust to low concentrations of pollutants, even low doses can adversely affect species already stressed by other chemicals, temperature changes and environmental factors. As aquatic organisms accumulate pollutants in their tissues and organs, they pass them on through the food chain-eventually endangering the health of birds, marine mammals and humans. While the Bay and Delta exhibit moderate pollution compared to some other estuaries in the nation, high levels of certain pollutants in certain areas are cause for concern.