In the 1930s, gambling ships anchored beyond the regulated three-mile limit, then kept measured from the beach. The ships were popular, and a fleet of ever-larger ships and barges appeared until the State Attorney General recalculated the limit to exclude the bay. The largest ship held the state police off for nine days with submachine guns in what the newspapers called The Battle of Santa Monica Bay.
Once a major commercial fishery, Santa Monica Bay's water quality declined drastically in the 20th century as development of Los Angeles County resulted in large amounts of sewage and trash-rich storm runoff being dumped into its waters. Through restoration projects mandated by the Clean Water Act and advocated by groups such as Heal the Bay and the Surfrider Foundation, the bay's water quality has improved fairly dramatically from its early-1980s nadir. Hyperion sewage treatment plant's output is now far cleaner than before. However, during the region's rainy winters, the bay suffers from algal bloom and other water pollution-related maladies, periodically forcing most of the famous beaches along its shore to close.
In 2006, game show host Peter Tomarken and his wife Kathleen were killed in a plane crash into the bay. They were heading to San Diego to pick up a cancer patient who needed transportation to UCLA Medical Center for treatment when their airplane crashed.
Since 2022, The Ocean Cleanup has been operating a cleanup system in Ballona Creek to prevent plastic and other solid waste from leaking into the bay.[3]
