It once looked like a swimming pool. From the wikipedia entry you linked:
"According to the USGS topographical map published in 1977, the area was approximately 0.25 km2 (62 acres). However, in recent years the pond has shrunk considerably. The maximum depth in 1993–1994 was described as "a foot deep" (30 cm). In January 1997, it was approximately 10 centimetres (3.9 in) deep; in December 1998 the pond was almost dry everywhere except for an area of a few tens of square meters."
"According to the USGS topographical map published in 1977, the area was approximately 0.25 km2 (62 acres). However, in recent years the pond has shrunk considerably. The maximum depth in 1993–1994 was described as "a foot deep" (30 cm). In January 1997, it was approximately 10 centimetres (3.9 in) deep; in December 1998 the pond was almost dry everywhere except for an area of a few tens of square meters."