A taskforce, made up of ACT government agencies, including Actew Corporation, the Commonwealth and surrounding NSW councils, has been working quietly since June on a vision for the salvation of the lake.

The plan calls for a co-ordinated and sustained culling program, for the first time, on the lake's European carp population.

The waters of the lake, which was envisaged by Canberra's designer, Walter Burley Griffin, as the ''playground of the city'', are in such a degraded state that the past several summers have been marred by extensive lake closures caused by toxic blue-green algae blooms.

The taskforce has called for treatment of waters flowing into the lake to prevent harmful nutrients, like phosphorous, getting into the lake, and that beneficial underwater and water's edge plants be planted or replanted.

There is also a plan for a co-ordinated attack on the population of the pest fish species, European carp, in the lake and its catchment water included targeting the areas, often away from the lake, where the fish gather to spawn.

There would also be a crackdown on Canberra builders who illegally allow sediments to run off their sites and into the stormwater system, efforts to control the flow of leaves and other organic matter into the city's drains and better management of pollutant traps.

Actew Water, Palerang and Queanbeyan Councils have agreed to step up efforts to prevent sewage spills and leaks while the possibility of flushing more water through the lake, particularly in the summer months, from the Googong Dam and the Captain's Flat Reservoir will also be explored.

But the solutions will not be quick or cheap, with the taskforce identifying up to 50 courses of action to be taken between now and 2030.

The taskforce was set up by Chief Minister Katy Gallagher in response to a report on the state of the lake by the ACT's Commissioner Robert Neil that found activities in the urban area surrounding the lake and not the ''usual suspects'' play the biggest role in the environmental problems of the troubled waterway.

Queanbeyan's sewage works, and catchment management in neighbouring NSW had traditionally been blamed for much of the lake's woes.

The taskforce brought together several ACT government agencies, the National Capital Authority, and the two cross-border councils to develop an 18-year plan to get the lake's water quality back to acceptable levels. The Cooma-Monaro Shire refused to take part, arguing that most of its land was outside the lake's catchment.

Talks were also held with land-care groups, lake-care volunteers and community members and the taskforce's report noted that no one believed the job would be done quickly or easily. There was also acknowledgement that one of the lake's intended purposes - that of a giant stormwater drain for the city - meant that it would be never be possible to develop it into a ''pristine'' waterway.