The Gulf of Carpentaria (14°S 139°E) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is generally defined as a line from Slade Point, Queensland (the northwestern corner of Cape York Peninsula) in the northeast, to Cape Arnhem, Northern Territory (the easternmost point of Arnhem Land) in the west.
At its mouth, the Gulf is 590 km wide, and further south, 675 km. The north-south length exceeds 700 km. It covers a water area of about 300,000 km². The general depth is between 55 and 66 metres (30 and 36 fm) and does not exceed 82 metres (45 fm). The tidal range in the Gulf of Carpentaria is between two and three metres. The Gulf and adjacent Sahul Shelf were dry land at the peak of the last ice age 18,000 years ago when global sea level was around 120 m below its present position. At that time a large, shallow lake occupied the centre of what is now the Gulf. The Gulf hosts a submerged coral reef province that was only recognised in 2004.