It may have looked like an attack by sharks, but the bright red waters of some of Australia's beaches Tuesday actually resulted from a much less menacing threat: algae.
A swimmer swims in the safety of the pool as a red algae bloom discolors the water at Sydney's Clovelly Beach on Nov. 27, 2012. Algae closed some beaches for swimming including Bondi Beach for a period of time.
A thick algae bloom known as noctiluca scintillans - otherwise known as "red tide" or "fire in the sea" -- began washing up
early Tuesday morning on beaches near Sydney.
A swimmer stops short of a red algae bloom at Sydney's Clovelly Beach on Nov. 27, 2012.
The bloom, which is likely caused by higher water temperatures and more movement in ocean currents, is not toxic, but swimmers were still advised to stay out of the water because it can cause skin irritation. The beaches that were closed reopened later in the day.