The Environment Agency will later today release a new map designed to show areas in England and Wales where viable hydropower resources are going untapped.

The hydropower opportunities and environmental sensitivities map forms part of a major new report from the agency, which found close to 26,000 locations where a hydropower turbine could generate renewable electricity.

The agency said that taken as a whole, these unused sites could generate about three per cent of the UK's renewable electricity needs by 2020, providing enough power for about 850,000 homes. However, it admitted that environmental considerations and grid constraints in remote locations meant that in reality the amount of power provided by hydropower was likely to be lower.

The map also seeks to rate the viability of the sites, identifying 5,000 locations where well-designed hydropower schemes that do not disrupt local fish communities could improve the area while generating zero-carbon electricity. It showed that stretches of the Severn, Thames, Aire and Neath provided particularly attractive sites for hydropower systems.