Lake Tuggeranong is polluted with toxic blue-green algae, prompting ACT authorities to issue an 'extreme alert'. The popular recreation spot was closed to swimming and other activities on Friday and the Environment Protection Authority said it would remain off limits until further notice. "As exposure to this level of blue-green algae carries an increased health risk, the water is closed to primary-contact recreation," a spokeswoman said. The lake is regularly closed for periods of time over summer as rising algae levels become hazardous. The most recent closure means Canberrans cannot swim in the lake, water ski or windsurf. Pet owners should not let their animals swim or drink the water. But experienced rowers, boaters, canoe users and fishermen can still take to the lake if they are informed of the algae risks and what to do if they come into contact with the water. In particular, contact with algae scum should be avoided, and clothing that has been in the water washed to remove any residue. The lake was closed about 3.30pm Friday and remained off limits as of Monday afternoon. Blue-green algae symptoms include rashes, headaches, fevers, gastroenteritis, seizures and respiratory failure, and those experiencing them were urged to see a doctor immediately.