Please answer the following question: Information:  - The Great Australian Bight is a large oceanic bight, or open bay, off the central and western portions of the southern coastline of mainland Australia.  - The Southern Ocean, also known as the Antarctic Ocean or the Austral Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. As such, it is regarded as the fourth-largest of the five principal oceanic divisions: smaller than the Pacific, Atlantic, and Indian Oceans but larger than the Arctic Ocean. This ocean zone is where cold, northward flowing waters from the Antarctic mix with warmer subantarctic waters.  - The Northern Territory (abbreviated as NT) is a federal Australian territory in the central and central northern regions of Australia. It shares borders with Western Australia to the west (129th meridian east), South Australia to the south (26th parallel south), and Queensland to the east (138th meridian east). To the north, the territory is bordered by the Timor Sea, the Arafura Sea and the Gulf of Carpentaria. Despite its large areaover , making it the third largest Australian federal divisionit is sparsely populated. The Northern Territory's population of 244,000 (2016) makes it the least populous of Australia's eight major states and territories, having fewer than half as many people as Tasmania.  - The Indian Ocean is the third largest of the world's oceanic divisions, covering (approximately 20% of the water on the Earth's surface). It is bounded by Asia on the north, on the west by Africa, on the east by Australia, and on the south by the Southern Ocean or, depending on definition, by Antarctica. It is named after the country of India. The Indian Ocean is known as "Ratnkara", ""the mine of gems"" in ancient Sanskrit literature, and as "Hind Mahsgar", ""the great Indian sea"", in Hindi.  - Western Australia (abbreviated as WA) is a state occupying the entire western third of Australia. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Southern Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east. Western Australia is Australia's largest state with a total land area of 2,529,875 square kilometres (976,790 sq mi), and the second-largest country subdivision in the world  however, a significant part of it is sparsely populated. The state has about 2.6 million inhabitants, around 11% of the national total. 92% of the population lives in the south-west corner of the state.  - The Blackwood River is a major river and catchment in the South West of Western Australia . The river begins at the junction of Arthur River and Balgarup River near Quelarup and travels in a south westerly direction through the town of Bridgetown then through Nannup until it discharges into the Southern Ocean at Hardy Inlet near the town of Augusta . The river has 41 tributaries including Dinninup Brook , Balingup Brook , St John Brook , Boyup Brook , Tweed River , Ti Tree Gully , Christmas Creek and Tanjannerup Creek . The upper or larger catchment area of the river is in agricultural areas , while the middle catchment area passes through forest areas , and the lower portion of the river passes into mixed forest , agricultural and residential lands . The river emerges into Flinders Bay at Augusta . It was discovered in 1827 by Captain James Stirling and named by Stirling after Vice-Admiral Sir Henry Blackwood , under whom he served as a Midshipman on HMS Warspite in 1808 -- 1909 during the Napoleonic Wars , in the North Sea and the Mediterranean . Historically it was of considerable importance in the early days of the Swan River Colony , and more recently of importance in the ecology of the Augusta - Margaret River region due to conflicts in land use policy . The upper catchment contains Toolibin Lake , a nature reserve and Ramsar site . Hardy Inlet has a number of islands -- namely Molloy Island and Thomas Island . The mouth of the river has attracted interest in its various points of opening and closing over the last 100 years , Duke Head at the west side being a benchmark location for the shifting mouth . The river is prone to occasional flooding . In 1945 it rose to the highest level recorded to that date , running 1.1 metres ( 3.6 ft ) over the Russell Street bridge in Nannup . The river flooded again in 1946 and 1947 closing roads but not causing any significant damage to towns along the river . In 1949 Nannup received 174 millimetres ( 6.85 in ) of rain in a period of seven hours , causing flooding ....    After reading the paragraphs above, we are interested in knowing the entity with which 'blackwood river' exhibits the relationship of 'mouth of the watercourse'. Find the answer from the choices below.  Choices: - arafura sea  - arctic ocean  - great australian bight  - indian ocean  - sea  - southern ocean  - timor sea
A:
indian ocean