Canberra's urban activity has been identified as the worst culprit for the degraded state of Lake Burley Griffin in a landmark study on the state of the waterway.

Commissioner for the Environment Robert Neil says in his report that it is activities in the urban area surrounding the lake and not the traditional ''usual suspects'' that play the biggest role in the environmental problems of the troubled waterway.

Mr Neil has found that rural activities, spills from Queanbeyan's sewage works, and catchment management in neighbouring NSW all play their part in the pollution of the lake.

But according to Mr Neil's long-awaited report, only sweeping changes to the way Canberra's urban catchment is managed, and the behaviour of its population, will make the iconic lake a viable recreational waterway again.

Mr Neil's three-volume report was commissioned in May 2011 after a summer of lake closures caused by toxic algal blooms and sewage spills and it calls for a concerted effort by the ACT Government, the National Capital Authority and cross-border catchment managers for permanent improvements to the lake's quality.

The report was tabled in the Assembly yesterday, on a day when the NCA announced another lake closure caused by dangerous levels of blue-green algae.

The commissioner found that ''urban storm water discharges'' during heavy rains were a major trigger for blue-green algal blooms and that ''without intervention there will be an increasing incidence of these conditions into the future.''

The report identified weedkillers used in suburban gardens, plant material from the city's residential areas washed into the storm water system and even faeces from household pets as contributors to the lake's water quality problems and called for a broadly-based policy response.

Actew has also been told that it needs to clean up its act, with leaks and seepage from ageing pipes also named as a cause of pollution in Lake Burley Griffin.

The commissioner made 17 recommendations for action to bring the lake back to health and tabling the report in the Assembly yesterday, Mr Corbell said that the government had already started work on some of the report's findings.

''We will work closely with the NCA to address the issues identified for Lake Burley Griffin,'' the minister said.

Mr Corbell also called on the community to begin to take precautions against allowing pollutant material into the lake's catchment.

''The commissioner has identified significant scope for Canberrans to take individual responsibility for actions that impinge on lake water quality,'' Mr Corbell said.

''Excessive use of fertilisers can easily be addressed by gardeners following manufacturers' instructions on application levels to reduce run-off nutrients into the lakes.

''Sewage and other spills should be immediately reported to Actew and emergency services.

''To reduce vegetation matter collecting in the lakes, leaves can be collected and used for mulch rather than be swept into street gutters to wash into the lakes and exacerbate oxygen depletion as they decompose.

''Excrement by pets should be collected and properly disposed of rather than left to wash into the lake.''

Greens MLA Shane Rattenbury, the man who moved the motion last year to commission the report, said yesterday that the report was important because it identified that the real source of the lake's problems lay away from the ''usual suspects.''

''Over the years, there's been a lot of debate around what the real problems where with the lake and one of the good things about having the inquiry was that we have now got to the bottom of it,'' Mr Rattenbury said.

''It has identified quite a lot of things that we do in the city that we can change… so it's clear that we can take steps to address those problems and the commissioner has identified those steps and given us a road map to fix the lake.''