More areas of Lake Burley Griffin have been closed to swimming after testing revealed "extreme" blue-green algae and bacteria levels in the lake.
The National Capital Authority on Thursday advised that Yarralumla Beach, Lotus Bay, the ferry terminal, east basin and central basin were closed to primary contact until further notice.
It comes after the authority closed areas of the Lake on Wednesday for the first time in the recreational season.
Weston Park east, Weston Park west and the central basin, which were closed on Wednesday, also remain closed.
The water-skiing area at Molonglo Reach is also closed due to heightened bacteria levels after heavy rain earlier in the week.
Extreme levels are defined as when there are 125,000 or more algae cells a millilitre, more than 25 times what is considered to be a low algal level.
"The affected areas of the lake will remain closed to primary contact until algae and bacteria levels have reduced to safe levels. Only experienced lake users can participate in secondary contact recreation activities, such as sailing, canoeing and rowing," a spokeswoman for the authority said.
The restrictions on secondary contact activities, which also include fishing and boating, are designed to make sure anyone near the water is informed of the algal risks, as well as lessen the likelihood of anyone falling into the lake.
A standing alert for heightened bacteria levels after heavy rain is also in place at Yarralumla Bay and Black Mountain Beach, which both remain open for swimming.
The Acton West Jetty area has a medium algae alert in place, which means the area is still open for primary contact but susceptible individuals could experience skin irritation.
Lake closures have already forced the organisers of a triathlon on Saturday to revert to a duathlon format, with competitors running twice in the event.
Canberra Triathlon Festival event director Mark Emerton said on Tuesday that health concerns had forced organisers to change the format of the event, which always had a plan B in place.
Two clear water quality tests must be taken in a row before lake areas can be reopened.
Water samples are taken each Monday from ten recreational sites around the lake between October and April.
Blue-green algae can quickly reproduce in conditions with abundant sunlight, slow-flowing or still water and sufficient levels of nutrients, particularly nitrogen and phosphorous.
The algae can cause skin and eye irritation and create toxins that damage liver and nerve cells.