The Oyster Harbour Catchment is situated along the South Coast of Western Australia and is a part of the South West Botanical Region. It stretches from Albany (Kinjarling) through to Tenterden, across the Stirling Ranges (Koikjenerruf) to Chillinup and South to, but not including, Two People Bay (Yelbering). The entire area is approximately 3000 square kilometres and includes populated centres of the City of Albany and the township of Mt Barker (Pwakkenbak), Porongurup (Borringgorrup) and Kendenup (Koin-den-up). There are a total of 48 sub-catchments contained within the Oyster Harbour Catchment.
The Oyster Harbour (Miaritch) is the centre catchment of the Albany Hinterland and shares its common borders with the Wilson Inlet Catchment to the West and Albany Eastern Hinterland to the East. These catchments fall into the South Coast Natural Resource Management Inc. area of responsibility that includes the South Coast, from Walpole in the West to Esperance in the East.