Ballast water discharge and the environment

Ballast water discharges by ships can have a negative impact on the marine environment.

Cruise ships, large tankers, and bulk cargo carriers use a huge amount of ballast water, which is often taken on in the coastal waters in one region after ships discharge wastewater or unload cargo, and discharged at the next port of call, wherever more cargo is loaded. Ballast water discharge typically contains a variety of biological materials, including plants, animals, viruses, and bacteria. These materials often include non-native, nuisance, exotic species that can cause extensive ecological and economic damage to aquatic ecosystems, along with serious human health issues including death.

There are hundreds of organisms carried in ballast water that cause problematic ecological effects outside of their natural range. The International Maritime Organization (IMO) lists the ten most unwanted species as:

The ballast tanks in New Zealand carry animals and plants that kill ecosystems. Ballast tanks are only used in cargo ships there. Ballast water is controlled under the Biosecurity Act 1993 in New Zealand.

A form of cholera, Vibrio cholerae, previously reported only in Bangladesh apparently arrived via ballast water in Peru in 1991, killing more than 10,000 people over the following three years.

The zebra mussel, which is native to the Caspian and Black Seas, arrived in Lake St. Clair in the ballast water of a transatlantic freighter in 1988. Within 10 years it had spread to all of the five neighbouring Great Lakes. The economic cost of this introduction has been estimated by the U.S. Fish and Wildlife Service at about $5 billion.

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Wikipedia