The ACT government said the water was also off limits for anything that involved putting a person's whole body in the water or submerging their head, including diving, waterskiing and windsurfing.

Rowing, fishing, boating and canoeing were still allowed, but the government warned that only experienced people who were aware of the risks and knew what to do if they came into contact with the water should consider going out on the lake.

The government said exposure to the level of blue-green algae carried an increased health risk, and warned pet owners not to let their animals swim in or drink the water.

Blue-green algae symptoms include rashes, headaches, fevers, gastroenteritis, seizures and respiratory failure. Anyone experiencing those systems was urged to see a doctor immediately.

The lake was closed on Wednesday, with updated alert levels and information available at www.environment.act.gov.au.

Meanwhile, Lake Tuggeranong has reopened for swimming after the Environment Protection Agency lowered its blue-green algae alert level to "low". It had been off limits since January 5.

The news comes as new water quality projects described as world-leading are being carried out at the University of Canberra, with the aim of improving the ACT's waterways.

Up to 5000 water samples from Lake Tuggeranong and the territory's urban ponds and wetlands will be analysed over an 18-month period, with researchers hoping to find out where nutrients like blue-green algae come from and how they behave once they are in the waterways.