GREEN algal blooms on Gladstone region's beaches have caused concern for some holiday-makers.

The bright green and purple blooms were seen at Tannum Sands and Agnes Water beaches on Tuesday.

Benaraby mum Karen Smith said lifesavers at the Tannum Sands beach told her children not to swim.

"(The lifesavers) said they were concerned because they didn't know what it was - but they hadn't closed the beach or anything," Ms Smith said.

"It looks like pollution ...and when you get close to it, it looks like paint."

And Ms Smith wasn't the only person to notice.

"I was talking to a family from Western Australia, and they were horrified - they just turned around and went home," Ms Smith said.

A Department of Environment spokesman said trichodesmium algae was common along the central Queensland coastline at this time of year.

"People should avoid direct contact with trichodesmium in the water and on the beach as it has the potential to cause skin and eye irritations," he said.

"On beaches trichodesmium usually breaks down and disappears over several days."

Lifesaving Queensland said if the algae was thick and widespread, the beach would have been closed as a last resort.

The organisation said people should ask surf lifesavers to make sure the water is safe to swim in.