A mysterious algal bloom at Jervis Bay is under investigation by NSW Fisheries and Shoalhaven City Council.
The green or turquoise coloured bloom was reported last week.
On December 10 council's environmental health staff assisted in taking water samples at Jervis Bay following reports of algal bloom.
A council spokesperson said NSW Fisheries sampled bloom offshore on Friday December 11.
"These samples were sent to ALS and University of Technology Sydney laboratories for analysis," the spokesperson said.
"Samples were collected at Callala Beach, Vincentia and Plantation Point as well as the middle of Jervis Bay.
"To identify the cause of the bright green/turquoise discolouration, samples will also be taken to test for nutrients such as total Nitrogen and total Phosphorus."
The results are due to be provided to Council by Friday, December 18.