A rare red alga has invaded the waves and sands of Bondi Beach, coming from off the coast of eastern Australia.
The thick bloom was caused by noctiluca scintillans, a dinoflagellate marine algae that is also called "Sea Sparkle" because it exhibits bioluminescence.
"As the algae die and sink in the shallow coastal water, they decompose, and oxygen is taken from the water column. This can lead to temporary low oxygen zones", explains Lauren Freeman from the Scripps Institution of Oceanography in San Diego.
Although the algae are naturally occurring, blooms such as these can be a hazard to swimmers.
High levels of ammonia contained in the algae can cause rashes and eye irritation.
These red tides reproduce quickly and have been seen in the Gulf of California and Monterey Bay, too.