The water was rich in sulphate of lime that was deposited onto the lake floor.
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Birridas are circular or oval in shape and range from 100 m to 1 km wide.
They commonly consist of a central, raised platform ringed by a moat-like depression.
Most birridas retain water for several months following rain.
Some birridas are connected to the sea by channels and receive seawater, where they form shallow bays.
These bays are important fish breeding and nursery areas, however, most birridas at Shark Bay are isolated.
