Water authorities were yesterday forced to issue a “precautionary” warning for the potentially toxic algae on the waterway.

Samples have been taken and results are expected within the next few days.

Yesterday water at the edge of the lake at Boathaven and the Lake Hume Resort was covered in a green scum floating on and below the surface.

Shores in the path of the north-east wind appeared most affected.

Chairwoman of the Murray Regional Algal Co-ordinating Committee, Natasha Ryan, said visual inspection indicated the scums could be toxic blue-green algae but laboratory analysis was needed for a positive identification.

She said routine monitoring had detected a number of unidentified scums at several locations throughout the lake.

“Scums on the water surface have been reported at Ludlows Reserve, Ebden Reserve, Kookaburra Point, Yacht Club Reserve, the dam wall, Hume Weir Park and Bellbridge Reserve,” Ms Ryan said.

“Given the large number of locations within the reservoir at which scums are present and the fact that many of these locations are popular recreational spots, the Murray RACC has issued this warning as a precaution.”

Ms Ryan said water users should use personal discretion when entering the water and should avoid any water that appears bright green, where obvious green scums are present, or a distinctive odour is noticeable.

“Many species of blue-green algae are potentially toxic and may cause gastroenteritis in humans if consumed and skin and eye irritations after contact,” she said.

“Boiling the water does not inactivate algal toxins.”

Last summer the near empty lake was plagued by blue-green algae blooms.

Red alert levels for Lake Hume, Lake Mulwala and the stretch of the Murray River in between were repeated from early February to April.

Three sites on Lake Hume — at the dam wall, Ebden and near the Bethanga Bridge — had tested positive for the algae and it had also been found in several river backwaters west of the dam wall.

The water authority yesterday said it would continue to monitor the situation and information updates about blue-green algae blooms and red level warning areas can be obtained from the freecall Algal Information Hotline on 1800 999 457.