The International Convention for the Control and Management of Ships' Ballast Water and Sediments (Ballast Water Management Convention) 2004, is an international maritime treaty which requires Signatory flag states to ensure that ships flagged by them comply with standards and procedures for the management and control of ships’ ballast water and sediments. The Convention aims to prevent the spread of harmful aquatic organisms from one region to another and halt damage to the marine environment from ballast water discharge, by minimising the uptake and subsequent discharge of sediments and organisms. From 2024 all ships are required to have approved Ballast Water Management Treatment System, according to the D2 standard (see below). Existing ships are required to install an approved system, which may cost up to 5 million USD per ship to install. To assist with implementation the IMO has released 14 Guidance documents in regards to the Convention including the G2 Guidelines for Ballast Water Sampling, G4 Guidelines for Ballast Water management and G6 Guidelines for Ballast Water Exchange.
The first scientifically recognised occurrence of a non-indigenous marine species being transported in ships water occurred in the North Sea in 1903, with the Asian phytoplankton Odontella appearing. The issue became more prevalent with the increase in shipping in the late 20th century and the issue was raised for the first time at the IMO in 1988. Following several years of development, the Convention was adopted by the International Maritime Organization in 2004.  To enter into force, the Convention required ratification by a minimum of 30 States, representing 35% of world merchant shipping tonnage, subject to which it would enter into force 12 months later. On 8th September 2016, Finland acceded to the Convention, bringing the contracting states to 52 and the combined tonnage of States to 35.14%. This triggered the applicability of the entry into force date of the Convention, which occurred on the 8th September 2017. Since Finland, a number of States have continued to accede, bringing the total as of 8th September 2017 to 66 contracting States, representing 74.89% of world merchant shipping tonnage.
All international going ships under the Convention must implement a ‘Ballast water management plan’ that enables the ship to manage their ballast water and sediment discharge to a certain standard. The plan is designed to meet the requirements for compliance with the Convention and the G4 Guidelines produced by the IMO. It includes standard operational guidance, planning and management, as well as additional details including sampling points and systems. Additionally all ships over 400GT must also carry a ballast water record book that details such requirements as the filling and discharge of each tank, according to time, date, location and the treatment applied to the water.
Ships that comply with the Convention will receive and are duly required to carry an international ballast water management certificate. To receive a certificate, a ship will have to supply the necessary documentation showing compliance with the Convention and a survey will be carried out on-board. A survey may be carried out by a flag State, or by a Classification Society who have been authorised by a flag State. The convention is monitored by Port State Control, who must assess the ballast water management plan and its operation on the ship.
Under the Convention, ships are required, according to a timetable of implementation, to comply with the D1 or D2 standards. The D1 standard requires ships to carry out a ballast water exchange, and specifies the volume of water that must be replaced.  This standard involves exchanging the uptaken discharge water from the last port, with new sea water; it must occur at a minimum of 200 nautical miles from shore. The D2 standard is more stringent and requires the use of an approved ballast water treatment system. The system must ensure that only small levels of viable organisms remain left in water after treatment so as to minimise the Environmental impact of shipping.
New ships will be required to install and comply with the D2 standard from the 8th September 2017, once the Convention has entered into force. Existing ships, who are subject to the phased implementation schedule, have potentially (depending on the renewal of their ship certificates) until the 8th September 2024, by which time all ships will comply with the D2 standard.
It is also possible for ships to discharge ballast at approved shore reception facilities in ports, as article 5 requires that when cleaning or repair of a ships ballast tanks occurs, ports should have adequate reception facilities for the sediments. Facilities must include safe disposal arrangements, storage and treatment equipment, safe and suitable mooring and emergency arrangements and the necessary reducers for connections to ships.
Some ships may be exempted from complying with the Convention, according to certain conditions and the appropriate permission being given by a flag State. These include ships trading in a limited area, small vessels including sailboats and fishing vessels, vessels only operating on one coast and also FPSOs.