In-water cleaning, also known as in-water surface cleaning, is a collection of methods for removing unwanted material in-situ from the underwater surface of a structure. This often refers to removing marine fouling growth from ship hulls, but also has applications on civil engineering structures, pipeline intakes and similar components which are impossible or inconvenient to remove from the water for maintenance. It does not generally refer to cleaning the inside of underwater or other pipelines, a process known as pigging. Many applications require the intervention of a diver, either to provide the power, or to direct a powered tool.
Depending on the reason for bottom cleaning, it may be desirable to capture and treat the waste dislodged from the surface. If the purpose is to remove potentially invasive alien species, then they must be removed from the water or killed. If the organisms are not a problem, it may be necessary to contain released toxins from the anti-fouling coating.
In-water cleaning of structures and vessels may distribute the surface contaminants in an area where they could be harmful. There are two main concerns:
Some cleaning technologies can cause significant damage or degradation of the substrate, particularly removal or excessive abrasion of protective or biologically active surface coatings. In some cases removal of the upper layer of an anti-fouling paint can expose paint which has a stronger concentration of active biocides, which can reactivate the paint.