India, Oct. 1 -- The mine closed in 1997 at the Western No. 5B, or WO5B, pit in Collie, Western Australia, leaving behind a large open mine void. The site is now known as Lake Kepwari, a recreational lake that supports activities such as swimming, boating and camping and reaches a maximum depth of about 65 meters. A case study published in the AusIMM Bulletin describes it as Western Australia's first successfully relinquished pit lake.

Collie lies about 160 kilometers south-southeast of Perth. More than 100 years of coal mining in the area has produced at least 13 pit lakes, all affected by acidic and metalliferous drainage. At WO5B, most reactive overburden and exposed coal seams were covered with waste rock. Parts of the mine-void edge...