It is against the law to introduce exotic organisms into California waters. Yet every day ships dump exotic species into the San Francisco Bay and Delta and southern California ports, amounting to hundreds of species and millions of organisms each year. Legislation concerning ballast water in Washington is less specific at the moment, and ballast water continues to be dumped in Washington waters, just as it is dumped daily into the waters of all other coastal states. At the start of a voyage, a ship may take on large quantities of water to achieve proper buoyancy and trim. Later when it is no longer needed, the waste ballast water is typically dumped on arrival at the destination port, sometimes thousands of miles from its source.
Studies show that ballast water carries a daunting variety of living marine or freshwater organisms.
Ballast water discharges have released Japanese gobies, New Zealand sea slugs, Black Sea jellyfish, dozens of Asian zooplankton species, possibly the Chinese mitten crab, and scores of other organisms into the San Francisco Estuary. The amount of foreign ballast water arriving at these ports will increase sharply with port expansions and with the projected rapid growth in international markets and trade. Many exotics that first arrive at these major shipping ports then spread or are reintroduced to other sites along the coast. The asian clam Potamocorbula was introduced by ballast water discharges into San Francisco Bay in 1986. Within a year it was the most abundant clam in the northern part of the system, filtering the entire water column twice a day, destroying phytoplankton blooms and disrupting the food webs that support fish in the Estuary.