International Mine Water Association Annual Conference 2012 McCullough, Lund and Wyse (Editors) | 287 The Collie Pit Lake District, Western Australia: An Overview Mark A. Lund 1* , Clint D. McCullough 1,2 , & R. Naresh Kumar 1 1 Mine Water and Environment Research Centre (MiWER), School of Natural Sciences, Edith Cowan University, 270 Joondalup Drive, WA 6027, Australia. 2 Golder Associates, West Perth, Western Australia 6005, Australia *Corresponding author: Phone: +61 8 6304 5644, Fax: +61 8 6304 5070, E-mail: m.lund@ecu.edu.au Abstract Open-cut mining can create pit lakes that form distinct lake districts. Localised factors at the lake level ensure that individual pit lakes develop different water qualities and ecological values. The Collie Lake District is formed from open cut coal mining operations in the south-west of Western Australia. The limnology and water quality of 13 of these lakes were investigated in 2009. All of the deep pit lakes appeared to be thermally stratified over the summer but many had, or were close to, mixing by autumn. The lakes were mainly Al buffered, with pH ranging from 2.5 to 6.4. Most lakes could be considered oligotrophic but some contained high N and moderate P concentrations. Dissolved organic C and metal concentrations were generally very low. Keywords: Water quality, biota, ecology, pit lake, end-uses, mine closure. Introduction On cessation of mining, open-cut voids that extend below the water table can fill with groundwater and surface runoff to form a pit lake. Mining operations can generate a number of pit lakes located relatively close together, forming a pit lake district; this has now occurred in a number of international mining regions (McCullough and Van Etten 2011). This paper focuses on a key Australian pit lake district where pit lakes uniquely cover the spectrum from abandoned without rehabilitation, to those with rehabilitated catchments approaching relinquishment back to the state for conservation, recreation or commercial development. Of the 16 pit lakes in Collie, of these, Ewington has been re-mined, Muja was unavailable and Black Diamond B is located on private property. The remaining 13 pit lakes were investigated in this study. Methods Study Site The town of Collie (population over 10,000) is located on the north western rim of the Collie coal basin within the Collie River catchment. Collie lies nearly 160 km south-southeast of Perth, and is the centre of coal mining in Western Australia (Figure 1). The Lake District is located in the Collie Coal Basin in Western Australia. The major land uses in the catchment are coal mining, timber production, power generation and agriculture. Approximately 79% of the catchment is state forest. The recreation and nature conservation values of the forest areas are highly regarded along with the recreational opportunities provided by the Wellington