The gypsum lakes of Shark Bay, or Birridas, have outstanding natural features and are a World Heritage Site. The most westerly point of the Australian continent is next to the Indian. Scattered around Shark Bay, especially within the Peron Peninsula inside Francois Peron National Park, are several saline lakes of gypsum. However, the most famous among locals is “Birridas.” Some birridas, like Big Lagoon, have seen marine invasions in more recent times, resulting in the formation of small inland bays.
It is believed that thousands of years ago, when sea levels were much higher than they are today, birridas were landlocked saline lakes among dunes. The water was so rich in sulfate of lime that it was deposited on the lake floor. But with the passage of time, when the sea level dropped, the lakes dried up gradually and created salty hollows, and the sulfate of lime evaporated and became loose, powdery gypsum. The shape of the gypsum lake “Birridas” is circular or oval and ranges from 100 m to 1 kilometer wide.
Gypsum lakes are frequently composed of an elevated platform in the center, surrounded by a depression resembling a moat. The central section corresponds to the level of the water table during the late Pleistocene Period, about 10,000 years ago. During very high winter tides or after heavy rains, when the groundwater level is raised, these moats fill with water to a shallow level.
Most birridas retain water for more than a few months following rain. And at those times, the dormant eggs hatch, and the birridas teem with brine shrimp, horseshoe crabs, and other invertebrates. They deliver a feast for wading birds such as red-necked stints and bar-tailed godwits that have migrated to Shark Bay from as far away as Siberia. Numerous birridas have channels leading to the sea, where they also take in seawater and create small bays.
These bays are extremely imperative for fish breeding and nursery areas, although most birridas at Shark Bay are isolated. But they are common in Francois Peron National Park, where there are over 100 on the east coast of the Peron Peninsula. You can see birridas when driving around the park; however, to appreciate the shapes and sheer number of birridas, it is paramount to take a flight.
