The potentially deadly blue-green algae outbreak in Lake Burley Griffin has reached levels that are more than 1000 times what is considered safe.

Water quality tests last week revealed unsafe levels of Anabaena circinalis, a potentially deadly strain of blue-green algae.

Contamination levels were at more than 66 million cells per millilitre last Thursday, compared with the 64,000 cells per millilitre earlier in the month.

The tender process for water quality testing and analysis at Lake Burley Griffin ends at the end of next month. The NCA will be looking for an organisation that offers the best value for money.

An NCA spokeswoman said the contract for water quality testing and analysis was put out for tender every few years.

She did not believe that the requirements of the contract had changed.

''It may be that the same people get it again,'' she said.

Water quality testing at Lake Burley Griffin is more rigorous during the summer. The same level of testing is not required during winter.

''There isn't the same level of testing because that is not when we usually have high instances of blue-green algae or bacteria,'' the spokeswoman said.

The lake will remain closed indefinitely, according to the National Capital Authority, and the results of the lake's latest water quality tests will be available tomorrow.

ACT Health advised the Anabaena circinalis strain of blue-green algae produced potentially deadly neurotoxins.

The authority has banned swimming and whole-body water contact activities at the lake. People have also been warned to keep their pets out of the water.