Discovery Bay is an open oceanic embayment lying along the coast of eastern South Australia and western Victoria in south-eastern Australia. Facing the Southern Ocean, Discovery Bay extends approximately 70 kilometres from Cape Northumberland, near Port MacDonnell, South Australia in the northwest, to Cape Bridgewater in the southeast, 20 k…Discovery Bay is an open oceanic embayment lying along the coast of eastern South Australia and western Victoria in south-eastern Australia. Facing the Southern Ocean, Discovery Bay extends approximately 70 kilometres from Cape Northumberland, near Port MacDonnell, South Australia in the northwest, to Cape Bridgewater in the southeast, 20 kilometres west of Portland in western Victoria. Cape Northumberland is the southernmost point of mainland South Australia. The Glenelg River is the principal inflow and enters the bay near the town of Nelson.