Canberra's main waterways, including Lake Burley Griffin, Lake Tuggeranong, Lake Ginninderra and Kambah Pool, have been closed due to high levels of blue-green algae.

Water quality expert Professor Ian Falconer said climate change would increase the number of harmful blue-green algae outbreaks.

''It's seasonal. These organisms are in the water all the time and they die back in the winter and multiply during the summer.

''They are related to water temperature so if you get a circumstance where you have a lot of water warming up and very little flow because of lack of rain they proliferate and they get to the point where they become a health hazard,'' he said.

Professor Falconer said improving water quality would lead to fewer algal blooms.

''The issue is that a lot of nutrients wash into the waterways particularly in urban areas, so you really have to cut down the nutrient load and it's a problem to do it.''

He said Canberrans needed to stop using phosphate-containing material, for example.

''A lot of the phosphorus for example that gets into the drains comes from phosphate containing detergents from washing powders and things like this.''

''All the lakes are really actually stormwater holding reservoirs they are not actually lakes at all. The water is held in by a dam and the natural flows particularly in the summer are very low so there aren't enough flows into the lakes to wash the nutrients out.'' He said people were unlikely to die from ingesting blue-green algae but they would get sick. ''It's killed a few dogs. We've had dog deaths from Lake Ginninderra and Lake Burley Griffin as a consequence of them swimming.'

Director of environment protection Robert Neil said blue-green algae was normal for time of year.

''We will continue to monitor all our lakes for the presence of blue-green algae and inform the public when there is any change,'' he said.