The naturally occurring blue-green algae Trichodesmium has been detected in lower estuaries of the Tweed.
The marine algae has been found in Cudgen Creek between the boat ramp and Cudgen Creek Bridge, and in the Tweed River adjacent to Togo Reserve at Tweed Heads.
There have also been reports from Jack Evans Boat Harbour and Terranora Creek.
Council's Senior Program Leader – Environmental Protection David Bell said Trichodesmium commonly bloomed in tropical and subtropical waters between August and December.
"As the temperature rises, we often see Trichodesmium along the Far North Coast at this time of year and a number of local government authorities are reporting blooms," Mr Bell said.
"While Trichodesmium is a blue-green algae, it can come in a lot of interesting colours including orange, grey, brown, green and purple. It can also give off an unpleasant 'fishy' smell."
Mr Bell said blooms of some Trichodesmium could produce toxins that pose a health risk.
"We are encouraging people to avoid swimming and surfing whenever there is a bloom and to keep animals away," he said.
"We are also advising that you don't eat shellfish from affected waters. If you come into contact with the algae, rinse it off with fresh water."
Trichodesmium is a member of the phytoplankton family and plays an important role in the aquatic food chain.
Calm conditions, northerly currents and warm water temperatures can increase growth.
Blooms disappear naturally.
Council's Smelly Creeks fact sheet offers additional information on Trichodesmium.
