Elterwater lake, a site of special scientific interest (SSSI) in the valley of Great Langdale, has been affected by blooms of blue-green algae since the 1980s, which threaten to crowd out other wildlife.

A new study has been launched by United Utilities, the Environment Agency and Natural England to determine the cause of the blooms, and what can be done to tackle them. The project is being delivered by aquatic scientists from APEM Ltd.

As well as performing painstaking fieldwork, APEM's scientists are trialling the use of aerial surveys of the lake's three interconnected basins. High resolution images are being captured from the skies over a period of months, to pinpoint subtle colour changes in each basin as the algae intensify.

The work is part of a wider programme by United Utilities, the Environment Agency and other partners to improve wildlife habitats and surrounding lakes and tarns in the Windermere catchment.

James Ellaway, Associate Director at APEM explained:

"Algal blooms can harm the plants, insects and fish that live in a lake by reducing the oxygen content of the water and by changing the water's chemistry.

"We are using state-of-the-art aerial photography and computer analysis software to get a picture of how Elterwater is changing. Combined with more traditional fieldwork, this process will give us a much clearer understanding of how and why the algae are produced, and the best way of caring for the lake in the long-term."

Elterwater has seen unusually high levels of algae in recent years, with an especially strong algal presence in the 'inner' of its three basins. Scientists believe this could be the result of an increase in phosphorus in the water, caused by a combination of fertiliser running off farmland into the lake, and a legacy from a period up to 1999 when treated wastewater from Langdale treatment works was discharged into the lake, under consent.

There are concerns that the algae could threaten the SSSI status of the lake, by crowding out rare plant species.

Pippa Smith, United Utilities' catchment manager said:

"We are pleased to be supporting this valuable study, which will allow a much clearer picture to emerge of the health of Elterwater, and any future steps required to aid its recovery.

"The use of aerial images, which is being pioneered by the APEM scientists, is especially interesting, as it could be used for future studies of this kind. The ability to take a snapshot from the sky means we can get a good idea of what is happening in the water, no matter how remote the location."

The study is part of the Windermere Catchment Restoration Programme partnership to improve water quality, natural wildlife and habitats for Elterwater and surrounding lakes and upland tarns in the Windermere catchment.

Elterwater contains a diverse range of habitats, including open water, swamp, fen and marshy grassland. Species dependent on the lake include water lobelia, water milfoil, yellow and white water lilies and the rare six stamened waterwart.