Dredged materials from built-up sediments around harbor entrances may be discarded into the ocean off Southern California in large quantities, if these sediments meet Ocean Dumping Act requirements. Dredged material can also be used for beach replenishment, landfill in harbors for new construction, or disposed of in sanitary landfill sites.

Two areas of historical sediment buildup and dredging activity are the Marina del Rey entrance channel and Redondo Beach King Harbor. Dumping of dredged materials can reintroduce buried contaminants into the ocean at the dumpsite. These can then be carried by currents into the Bay.

There is currently one permitted ocean dump site nearby the Bay. Known as LA-2, this site receives dredge materials from maintenance and construction activities at Los Angeles and Long Beach harbors that must be tested for toxicity. If found to be toxic, the dredge spoils cannot be disposed of at this site.

Prior to 1972, there was also dumping of the pesticide DDT from the Montrose Chemical Company at a site (known as LA-1) in the San Pedro Channel 10 miles northwest of Catalina Island in 2500 feet of water. Some DDT and other industrial wastes may also have been illegally dumped before reaching the LA-1 site. Because of the damage DDT causes to the environment, the use of DDT is now outlawed in the United States.