More than a thousand tankers pass under the Golden Gate Bridge each year, along with countless container ships, recreational boats, and other vessels. Numerous oil refineries, tanks, and pipelines also line the bay. Each of these could cause an oil spill. Oil is extremely toxic to marine life even at very low concentrations. On top of this, the bay's coastal wetlands are particularly vulnerable to spills. Nevertheless, no data on oil spills in the bay are available. But data for California as a whole show that the number of spills has fluctuated since 1990. The volume of oil spilled dropped sharply in 1991, but has been fluctuating since.

Findings
Unable to find annual oil-spill data specific to San Francisco Bay, NRDC researchers examined the number and severity of oil spills in California between 1990 and 1999, as reported by the U.S. Coast Guard. Since the passage in 1990 of the federal Oil Pollution Act and California's Spill Prevention and Response Act, there has been a modest drop in the number of spills -- 651 in 1999 compared with 688 in 1990 -- although the number of spills varied from year to year. Far more dramatic was the change in the volume of oil spilled: From 1990 to 1991, it dropped sharply, from 434,993 gallons to 56,531 gallons. Since 1991, the volume has fluctuated. In 1999, 77,139 gallons were spilled. Given the lack of specific information about spills in San Francisco Bay, it is difficult to draw conclusions from these statistics about oil's effects on, and dangers to, the region.