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Ballast Water

Ballast water is one of the major pathways for the introduction of nonindigenous marine species. Ballast water is fresh or saltwater held in the ballast tanks and cargo holds of ships. It is used to provide stability and maneuverability during a voyage when ships are not carrying cargo, not carrying heavy enough cargo, or when more stability is required due to rough seas. Ballast water may also be used to add weight so that a ship sinks low enough in the water to pass under bridges and other structures.

Usually, ballast water is pumped into ballast tanks when a ship has delivered cargo to a port and is departing with less cargo or no cargo. Ballast water is then transported and released at the next port-of-call where the ship picks up more cargo. If a ship is receiving or delivering cargo to a number of ports, it may release or take on a portion of ballast water at each port. In such cases, the shipís ballast water contains a mix of waters from multiple ports.

The release of ballast water may introduce non-native organisms into the port of discharge. These introduced species, or bioinvaders, are also referred to as exotic species, alien species, and nonindigenous species. (Source: Massachusetts Institute of Technology Sea Grant - Ballast Water)

Ballast water release

Discharge of ballast water from cargo ship


  • Balancing Act: A Policy Success Story in the Great Lakes

    • Feb 23, 2024
    • Michigan State University. Michigan Sea Grant.

    • The Great Lakes remain one of the most heavily invaded freshwater systems in the world. Ballast water from cargo ships crossing the ocean inadvertently brought in many aquatic invasive species (AIS), accounting for the introduction of 40% of all nonindigenous aquatic species in the Great Lakes. However, collaborative efforts have led to pioneering research and policy changes that have reduced this threat.

  • Recreational Craft and Invasive Species: How to Manage Biofouling to Stop the Spread

    • Oct 13, 2022
    • International Maritime Organization.

    • Invasive aquatic species are known to be one of the biggest drivers of biodiversity loss, and their management especially in marine environments is incredibly challenging. To tackle this issue, the GloFouling Partnerships, led by the International Maritime Organization (IMO) and in collaboration with the International Council of Marine Industry Associations (ICOMIA), World Sailing, and the International Union for Conservation of Nature (IUCN), has published a new Biofouling Management for Recreational Boating Report [PDF, 13.4 MB]. The aim of the report is to stop the spread of invasive aquatic species which can adhere to hulls and other areas of recreational craft by addressing how to manage biofouling.

  • Addressing Invasive Species in Ships' Ballast Water - Treaty Amendments Enter into Force

    • Oct 14, 2019
    • International Maritime Organization.

    • Amendments to an international treaty aimed at preventing the spread of potentially invasive species in ships' ballast water entered into force on 13 October 2019. The International Convention for the Control and Management of Ships' Ballast Water and Sediments, 2004 (the BWM Convention) was adopted by the International Maritime Organization (IMO), a specialized agency of the United Nations, to address this problem. The BWM Convention entered into force in 2017. The amendments formalise an implementation schedule to ensure ships manage their ballast water to meet a specified standard ("D-2 standard") aimed at ensuring that viable organisms are not released into new sea areas, and make mandatory the Code for Approval of Ballast Water Management Systems, which sets out how ballast water management systems used to achieve the D-2 standard have to be assessed and approved. This will help ensure that aquatic organisms and pathogens are removed or rendered harmless before the ballast water is released into a new location – and avoid the spread of invasive species as well as potentially harmful pathogens.

Selected Resources

The section below contains highly relevant resources for this subject, organized by source.

  • Ballast Water - Pacific Ballast Water Group

    • Pacific States Marine Fisheries Commission. Western Aquatic Invasive Species Resource Center.

  • GloBallast Partnerships Programme

    • GloBallast Partnerships Programme.

    • Building Partnerships to Assist Developing Countries to Reduce the Transfer of Harmful Aquatic Organisms in Ships’ Ballast Water, simply referred to as GloBallast Partnerships (GBP), was initiated in late 2007 and is intended to build on the progress made in the original project. This was initially planned as a five-year project, from October 2007 to October 2012, but was extended until June 2017.

  • GloFouling Partnerships

    • International Maritime Organization; United Nations Development Programme; Global Environment Facility.

    • GloFouling Partnerships is part of the wider efforts by the International Maritime Organization (IMO), in collaboration with the United Nations Development Programme (UNDP) and the Global Environment Facility (GEF), to protect marine ecosystems from the negative effects of invasive species. This work began in 2001 under the GloBallast Programme.

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