Ballast Water


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Open-ocean ballast water exchange

Photo 82: Open-ocean ballast water exchange
National Ballast Information Clearinghouse

Ballast water is water that is taken on by a vessel to compensate for changes in the vessel’s weight as cargo is loaded or unloaded, and as fuel and supplies are consumed. When a vessel takes on ballast water, whether freshwater or saltwater, organisms found in that water are typically taken in as well. These organisms, often referred to as aquatic nuisance species, are carried in the ballast tanks of the vessel until it arrives at its next port where, due to changes in the distribution of the vessel’s cargo, the organisms may be released into a new ecosystem, establish viable populations, and prey on or outcompete indigenous species. The introduction of aquatic nuisance species can alter entire ecosystems and is considered one of the greatest threats to the world’s oceans.

The discharge of ballast water from vessels is the single largest vector for the transmission of aquatic nuisance species worldwide. For example, Chinese mitten crabs, originally native to Northern Asia, were introduced via ship ballast water into the marine environment off the West Coast of the United States and have had devastating biological and economic effects. Aquatic nuisance species are estimated to cost the U.S. $137 billion per year.