Visitors noted a “fishy smell” on Tuesday morning, saying the crimson waters looked like “tomato sauce.” By mid-morning, the algae bloom had closed Bondi and several other beaches in and around Sydney, including Clovelly Beach in Randwick, as health officials warned that high ammonia levels in the water could be harmful.
“There are some possible risks to human health from red algae including skin rashes and eye irritation, and for this reason the beach will remain closed until the algae dissipates,” the Randwick City Council said in a statement.
The rare red tide is also known to cause fish kills and make seafood in the area like shellfish harmful to eat.
The Metropolitan Sydney South Coast and Hunter Regional Algal Coordinating Committees issued an alert late Tuesday identifying the bloom as Noctiluca scintillans, “which appears pinkish or reddish in water with a similar characteristic to fairy floss.” The committee noted that it can also appear phosphorescent at night.
Algal blooms are more common during the spring and fall when there are higher water temperatures and greater movements of the ocean currents, according to a spokesman for the NSW Office of Water. Scientists believe Tuesday’s red tide may be the result of an upwelling of colder nutrient-rich deep ocean water onto the continental shelf.
Another algal bloom was spotted in Botany Bay, south of Bondi last Friday. Officials hope the current red tide will dissipate by the weekend, when temperatures are expected to reach 40 Celsius (104 Fahrenheit).