Information:  - A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.  - An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.  - An ocean (the sea of classical antiquity) is a body of saline water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean, which covers almost 71% of its surface. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans. The word "sea" is often used interchangeably with "ocean" in American English but, strictly speaking, a sea is a body of saline water (generally a division of the world ocean) partly or fully enclosed by land.  - The River Torrens is the most significant river of the Adelaide Plains and was one of the reasons for the siting of the city of Adelaide, capital of South Australia. It flows from its source in the Adelaide Hills near Mount Pleasant, across the Adelaide Plains, past the city centre and empties into Gulf St Vincent between Henley Beach South and West Beach. The upper stretches of the river and the reservoirs in its watershed supply a significant part of the city's water supply. The river's long linear parks and a constructed lake in the lower stretch are iconic of the city.  - Adelaide city centre is the innermost locality of Greater Adelaide, the capital city of South Australia. It is known by locals simply as ""The City"" or ""Town"" to distinguish it from Greater Adelaide and from the City of Adelaide (which also includes North Adelaide and the parklands). The locality is split into two key geographical distinctions: the city "square mile", bordered by North, East, South and West Terraces; and the section of the Adelaide Parklands south of the River Torrens which separates the built up part of the city from the surrounding suburbs and North Adelaide.   - A sea is a large body of salt water that is surrounded in whole or in part by land. More broadly, "the sea" is the interconnected system of Earth's salty, oceanic watersconsidered as one global ocean or as several principal oceanic divisions. The sea moderates Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. Although the sea has been traveled and explored since prehistory, the modern scientific study of the seaoceanographydates broadly to the British "Challenger" expedition of the 1870s. The sea is conventionally divided into up to five large oceanic sectionsincluding the International Hydrographic Organization's four named oceans (the Atlantic, Pacific, Indian, and Arctic) and the Southern Ocean; smaller, second-order sections, such as the Mediterranean, are known as "seas".  - The Onkaparinga River is a river located in South Australia south of the Adelaide city centre . It runs from its source between Mount Torrens and Charleston in the Mount Lofty Ranges , and flows south westerly to an estuary at Port Noarlunga . The catchment is over 500 square kilometres ( 190 sq mi ) in area , and in part includes the following protected areas - the Encounter Marine Park , the Onkaparinga River National Park , the Onkaparinga River Recreation Park and the Port Noarlunga Reef Aquatic Reserve . The Onkaparinga River is the second major river within the Adelaide metropolitan area , after the River Torrens . The name derives from the Indigenous Kaurna name Ngangiparri which translates as `` The Women 's River '' . In 1837 Surveyor General Col William Light named it Field 's River , or the Field River , after Lieut William George Field RN ( 1804 - 1850 ) of the brig Rapid , who carried out the first surveys in the vicinity of its estuary , but subsequent Governor George Gawler soon reinstated the Indigenous name . The first Europeans to explore its sources and the Onkaparinga Valley were the party of Dr. George Imlay and John Hill in January 1838 . It is a source of fresh water for Adelaide . Mount Bold Reservoir was constructed between 1932 and 1938 along a section of its path approximately 20 kilometres ( 12 mi ) inland . Much of its flow is diverted via a tunnel from the Clarendon Weir to the Happy Valley Reservoir , that in turn supplies some 40 per cent of Adelaide 's water supply . Most years the flow to the reservoir is supplemented by water pumped from the River Murray via a pipeline from Murray Bridge .    After reading the paragraphs above, we are interested in knowing the entity with which 'onkaparinga river' exhibits the relationship of 'mouth of the watercourse'. Find the answer from the choices below.  Choices: - gulf st vincent  - sea  - southern ocean
Answer:
gulf st vincent