The alert was issued on October 29, where WaterNSW advised locals not to undertake recreational activities where they may come into direct contact with the water.

In terms of park visitors, this only applies to swimmers, so those sailing on their vessels haven't needed to worry.

This is great news for park manager Leith Smith, who said the red alert hadn't impacted visitor numbers yet.

"We've still got the water park which is recycled water and it doesn't come from the dam," Mr Smith said.

"Everybody has still been using their boats and things like that.

"The benefit of blue green algae is we actually have water."

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Blue-green algae appears as green paint-like scums on the water, near the edges, or as greenish clumps through the water, according to WaterNSW.

"It makes the water appear dirty, green or discoloured and generally has a strong musty or earthy odour," a statement said.

"People should not eat fish, mussels or crayfish from red level warning areas.

"Blue-green algae occur naturally and can reproduce quickly in favourable conditions where there is still or slow-flowing water, abundant sunlight and sufficient levels of nutrients."

Mr Smith said he was unsure of when the red alert would be lifted.

"Depending on the weather, the winds, as far as I know it can take a week ... three weeks, it's just one of those things that we hope it goes away soon," he said.

"I don't know how much more the heavens can throw at us, we've been through so much."

WaterNSW will continue to monitor the dam and the alert will be lifted when the algae dissipates.

The dam is at 26.7 per cent as of Friday, having risen up after recent rainfall.