In-water cleaning of vessels can manage biofouling to optimise the performance of vessels and other movable structures and to minimise biosecurity risks. However, in-water cleaning can physically damage some antifouling coatings, shorten coating service life and release a pulse of biocide into the environment.
In-water cleaning can also facilitate release of invasive marine species (IMS) into the surrounding environment.
Therefore, this treatment should only be undertaken when removal of biofouling presents an acceptable biosecurity risk, does not harm the antifouling coating on the vessel and the risk of contaminant release from the surface is determined as acceptable by the relevant authority.
Fisheries is the lead for aquatic biosecurity in Western Australia. Its policies relating to in-water cleaning have recently been reviewed. Fisheries recommends that cleaning companies considering undertaking in-water cleaning of vessels take the steps detailed in the new 
guidance statement. This will reduce the likelihood of transferring live non-endemic or noxious fish (including IMS) into or within WA, which would be contrary to the Fish Resources Management Act 1994.
Although this guidance statement recommends the use of in-water cleaning in some circumstances, vessels should be removed from the water for cleaning and maintenance in preference to in-water operations, where this is operationally practicable. In-water cleaning should not be considered a replacement for coating maintenance and renewal at shore-based maintenance facilities.
For further advice on in-water cleaning, please email biosecurity@fish.wa.gov.au