London has a combined sewerage system, built by the Victorians to handle sewage but only a limited amount of rainfall. Due to its limited capacity, the sewers were designed to overflow into the River Thames during periods of heavy rainfall. The skimmer boats will screen out the litter left from these sewer discharges. 

The Skimmers follow on from the Thames Tideway Strategic Study in 2000 which was set up to consider he environmental impact of storm discharges to the tidal Thames and to propose potential solutions. It recommended improvements to the existing sewage treatment works and the building of a storage and transfer tunnel that would take storm sewage to East London for treatment. Recognising that the tunnel would be a longer term solution, Thames Water commissioned the Skimmer vessels.

The vessels, which are the first of their type in the world, mark the first phase of Thames Water's programme to improve the environmental and aesthetic quality of the River Thames. Officially Damen Skimmer 2408s, the 24m LOA vessels are specially designed to navigate London’s bridges. In operation they clear the upper layer of river water from floating debris by means of two rotating skimmers. Screens sit 450mm deep below the river surface and debris is directed onto them by the inner hulls of the vessel, where it is picked up by the mechanical screening equipment and conveyed to the rear of the vessel where it is drained ready for disposal in to a refuse barge.

At the commissioning ceremony on 12 September Thames Water chief executive David Owens said, 'Sewage in the Thames can have a real impact on people’s enjoyment of the river, as well as on water quality and wildlife. These skimmer boats are a significant step forward in improving the quality of the river following occasional sewage discharges, which are currently inevitable due to the design of London’s sewer network.'

The Skimmer vessels are an interim measure to improve the quality of the River Thames. They are part of a £500+ million investment programme to improve the quality of the tidal Thames, which includes a £400 million upgrade programme for London’s major sewage treatment works. In the longer term, the UK Government has approved plans for the Tideway Tunnel, which will intercept sewage from the existing sewage overflow points.