Estuaries have high concentrations of particles suspended in the water. The suspended particles absorb sunlight required for plant photosynthesis and they give color to the water. The suspended sediments can eventually sink and become deposited on the Bay's sea floor. Some toxic contaminants attach onto particles and are carried with the sediments by water currents. We measure the concentration of particles in water as total suspended solids, or TSS. Within the Bay-Delta system, TSS concentrations range from a low of 1-2 milligrams per liter (mg/liter) to maximum concentrations that occasionally exceed 1,000 mg/liter.

Description of Numbered Regions:
1. During periods of high Delta outflow, such as in early 1993, large quantities of suspended sediments are carried into the Bay from the Sacramento and San Joaquin Rivers. The water can become very turbid during these periods of rapid sediment input.
2. During years of low Delta outflow, such as 1994, sediment inputs are reduced and the concentrations of suspended sediments are smaller. So the turbidity, and the color, of Bay waters changes over time because the concentrations of suspended solids change from season to season and from year to year.
3. The concentrations of suspended sediments are smallest in the Central Bay (the region of the Bay-Delta that is farthest from the river sources of sediments). For this reason, Bay waters often appear green near San Francisco but brown in Suisun Bay.
4. The small local streams that flow into the South Bay also carry sediments. During the intense storms of early 1995 these stream inputs greatly increased the concentrations of suspended solids in the South Bay, especially in the region below the San Mateo Bridge.
5. During very wet years, such as 1995, the Bay waters are turbid throughout the year because of sustained riverine inputs of suspended sediments.