There have already been a number of blue-green algal blooms across the state due to the unseasonably hot weather and low flows in some rivers and streams.
On the north coast there is currently an algal bloom ay Baywood Chase Pond at Byron Bay.
The NSW Water Commissioner, David Harriss, said if residents notice an algal bloom they should report it.
"Individuals and families should be aware of any current algal alerts before swimming in lakes, dams, rivers and at the beach," he said.
"I would also encourage people to learn the basics of how to identify an algal bloom and who to alert if they notice a bloom in a local waterway."
Mr Harriss said that algal cells are a natural part of aquatic ecosystems that are always present in the water - usually in small, harmless numbers.
"These cells can multiply and grow, or 'bloom' when there is the right combination of environmental conditions, including high nutrient levels, warm water temperatures, sunlight and still water."
Algae scums are most often blue-green or green.
Information updates about the status of blue-green algae are available on the NSW Office of Water website.
The Office of Water, in conjunction with other state agencies, local councils and community volunteers, conduct routine monitoring of water quality in the state's major dams and rivers.
© ABC 2013
16:41 EDT Lightning strikes sparked fires in the roof spaces of two Canberra houses today as storms swept through the capital.