The National Capital Authority has an lengthy run down on the state of Lake Burley Griffin:
Black Mountain Beach and Weston Park (East and West) in Lake Burley Griffin are currently closed to primary contact recreation due to high levels of blue-green algae.
At present, the blue-green algae levels are at the Extreme Alert Level. The water is closed to primary contact recreation as exposure to this level of blue-green algae carries an increased risk of adverse health effects.
Primary contact recreation means recreation that involves whole-body water contact or submersion of the head. Examples include swimming, diving and windsurfing.
Secondary contact recreation (such as rowing, fishing, boating and canoeing) will still be permitted, noting ACT Health’s advice
The West Basin also has a medium alert.
Having said that I was swimming at Acton on Australia Day and am no sicker nor more dead than I was before.