COLUMBIA, S.C. (WCBD) – Swimmers and boaters in South Carolina should be on the lookout for dangerous algal blooms during warm weather months.

State health officials are warning citizens to watch out for the harmful blooms which can be in surface waters of natural, untreated rivers and lakes.

According to the South Carolina Department of Health and Environmental Control, these blooms happen when tiny plant-like organisms called algae and cyanobacteria overgrow in rivers, lakes, and oceans. They can be associated with foam, scum, or thick layers of algae on the surface water.

Health leaders say the blooms can look and smell bad. They may cause the water to appear green, red-brown, or blue. “Some algal blooms are formed by species that can produce toxins. When they contain toxins that affect the health of people, animals, and the environment, they are known as harmful algal blooms (HABs),” DHEC said.

“If you’re planning on recreating in a water body, we advise you to visually inspect the water before going in,” said Emily Bores, DHEC’s HAB Coordinator. “If you notice a foul smell or discoloration, it’s best to err on the side of caution and stay away. Remember, when in doubt, stay out.”

State health leaders said HABs are more likely to occur in late spring to early fall when water temperatures are warmer and there is increased sunlight.

While you cannot tell if a bloom is harmful just by looking at it, if an algal bloom is suspected, health officials say you should keep yourself and your pets away from the area.

To notify DHEC of a bloom in the state’s lakes, rivers, streams or estuaries, contact the HAB hotline at 803-898-8374 or email the HAB Coordinator at boreseb@dhec.sc.gov.