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.
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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.