In 1991, the IMO adopted guidelines which recommend that ships should avoid taking on
ballast in shallow areas and during toxic blooms
of marine algae; keep accurate records
of where and when
ballast is loaded;
exchange ballast water at sea, where toxic organisms are rare; and discharge sediments into approved areas at the port
of destination («End
of the line for deadly stowaways», New Scientist, 24 October 1992).