The State Water Resources Control Board (SWRCB) assesses the quality of surface water bodies. Due to the volume of these water bodies, they cannot be assessed on a consistent basis statewide and tend to be assessed if problems are known or suspected. For these reasons, trend analysis is not currently possible for surface water quality. Data from 1992 indicate the following:
| WATER BODY TYPE | ASSESSED | TOTAL SIZE | GOOD | INTERMEDIATE | IMPAIRED | UNKNOWN |
| Rivers and Streams | 18,846 miles | 203,313 miles | 22% | 36% | 21% | 21% |
| Lakes | 912,837 acres | 1,177,634 acres | 18% | 37% | 25% | 20% |
| Estuaries, Bays, and Harbors | 465,172 acres | 465,172 acres | 6% | 8% | 75% | 11% |
| Ocean and Open Bays | 834 miles | 1,840 miles | 89% | 8% | 3% | 0% |
The SWRCB also collects data on contaminants in fish and mussel tissue. Unfortunately, these data are not collected in a random manner and are also not suitable for trend analyses.
The primary source of data maintained by the SWRCB which is appropriate for use as an environmental indicator is data on the rate of occurrence and remediation of leaking tanks.
The number of leaking underground storage tanks reported is
decreasing, while increasing numbers of leaking tanks are
being cleaned up.
The number of leaking tanks reported each year peaked in
1990 followed by a significant decreases in subsequent
years. This decrease may be due to technological increases
in the construction of double-walled underground tanks which
are much less susceptible to leaks. At the same time, the
number of leaking tanks cleaned up has been steadily
growing.