Different techniques used.
Although the sea can sometimes complete clean-up with remarkable efficiency, final clean-up is very often justified, for ecological, economic or aesthetical reasons. Once the bulk of the pollution has been removed and all risk of new arrivals of pollutant eliminated, the second phase of clean-up can begin.
The basic principle underlying final clean-up is to take advantage as much as possible of natural cleaning processes, or to replace these processes if they prove to be inexistent or inefficient. A wide range of techniques has been developed, of which some also feature in initial clean-up. These techniques cannot systematically be applied to all substrates, but should be defined according to the characteristics of the site, the pollutant, the type of arrivals and the quality of clean-up required. The ecological sensitivity of the site and its surroundings must of course be taken into consideration when selecting a technique and determining the level of clean-up to be attained.