Australia possesses 25,760 kilometers of coastline according to Geoscience Australia measurements, making it the sixth-longest national coastline globally. The continent is bounded by three oceans: the Indian Ocean to the west and south, the Pacific Ocean to the east, and the Southern Ocean to the south. Bass Strait, measuring approximately 240 kilometers at its widest point, separates the mainland from Tasmania and connects the Tasman Sea to the waters south of the continent. Torres Strait, spanning roughly 150 kilometers between Cape York Peninsula and Papua New Guinea, contains more than 270 islands and serves as the northern maritime boundary.
The Great Barrier Reef extends 2,300 kilometers along the Queensland coast from the Torres Strait to just north of Bundaberg. This reef system comprises approximately 2,900 individual reefs and 900 islands covering an area of 344,400 square kilometers. UNESCO designated it a World Heritage Site in 1981. The reef supports over 1,500 fish species, 411 hard coral species, and approximately 30 species of whales and dolphins according to the Great Barrier Reef Marine Park Authority. Water temperatures in the reef zone range from 24°C in winter to 29°C in summer. Coral bleaching events occurred in 1998, 2002, 2016, 2017, 2020, and 2022, with the 2016 event affecting approximately 93 percent of individual reefs to some degree according to the Australian Institute of Marine Science.
Ningaloo Reef on the Western Australian coast stretches 260 kilometers from Red Bluff to Exmouth Gulf. Unlike the Great Barrier Reef, Ningaloo runs directly adjacent to the coast, in some locations less than 100 meters from shore. The reef became a World Heritage Site in 2011. Between March and July each year, whale sharks aggregate at Ningaloo in predictable numbers, with the Western Australian Department of Biodiversity documenting between 300 and 500 individual sharks during peak season. The continental shelf drops away rapidly beyond Ningaloo, creating conditions where humpback whales migrating north pass within several kilometers of shore between June and November.
The Murray River flows 2,508 kilometers from its source in the Australian Alps to its mouth at Lake Alexandrina in South Australia. The Darling River, measuring 1,472 kilometers, is the Murray's longest tributary. Together these rivers drain approximately one-seventh of the Australian continent, covering an area of 1,061,469 square kilometers across Queensland, New South Wales, Victoria, and South Australia. The Murray-Darling Basin Authority reports that average annual flow at the Murray mouth is approximately 767 gigaliters, though this varies substantially between years. Flow has declined approximately 40 percent since European settlement according to Commonwealth Scientific and Industrial Research Organisation analysis published in 2008. Zero flow days at the mouth, once rare, occurred on 40 percent of days between 1997 and 2010. The basin supports agricultural production worth approximately $24 billion annually according to 2020 figures from the Murray-Darling Basin Authority.
Sydney Harbour, known formally as Port Jackson, extends 19 kilometers inland from the Tasman Sea and covers 55 square kilometers at high tide. The harbor contains approximately 240 kilometers of shoreline when all bays and inlets are measured. Maximum depth reaches 47 meters near the Harbour Bridge. Captain James Cook sailed past the harbor entrance on April 29, 1770, but did not enter. Captain Arthur Phillip, commanding the First Fleet, sailed into Port Jackson on January 26, 1788, establishing the first European settlement at Sydney Cove. The Sydney Harbour Bridge, completed in 1932, spans 503 meters across the harbor with its arch rising 134 meters above mean sea level. The Sydney Opera House, completed in 1973, sits on Bennelong Point where the harbor meets Farm Cove. Ferry services carry approximately 15 million passengers annually across the harbor according to Transport for New South Wales data from 2019.
The Great Australian Bight forms a large open bay on the southern coastline, extending approximately 1,160 kilometers from Cape Pasley in Western Australia to the Eyre Peninsula in South Australia. The Bight is part of the Southern Ocean, with the continental shelf extending 30 to 70 kilometers offshore before dropping away to the abyssal plain at depths exceeding 5,000 meters. The Bunda Cliffs along the Nullarbor Plain rise up to 60 meters directly from the ocean, forming one of the longest unbroken sea cliff systems in the world at approximately 100 kilometers. Southern right whales calve in the Bight waters between May and October, with the Head of Bight observation area recording peak whale numbers typically in September. The Australian Government rejected a proposal from energy company BP to drill exploration wells in the Bight in 2016, and Equinor withdrew its application in 2020.
Fraser Island, known by its traditional name K'gari, is the world's largest sand island, measuring 123 kilometers in length and covering 166,038 hectares. The island lies off the Queensland coast approximately 200 kilometers north of Brisbane. Sand depths on the island exceed 200 meters in some locations. The island contains more than 100 freshwater lakes, including 40 perched lakes that sit on layers of organic matter above the water table. Lake McKenzie, a perched lake approximately 150 meters above sea level, contains water with a pH of 4.5 to 5.5, too acidic for most aquatic life. Rainforest grows directly from sand on the island, a rare ecological phenomenon. UNESCO inscribed the island on the World Heritage List in 1992. A bushfire burned approximately 87,000 hectares of the island between October 2020 and January 2021.
The Whitsunday Islands comprise 74 islands located between the Great Barrier Reef and the Queensland coast. Most of the islands are uninhabited national park land. The Ngaro people inhabited the islands for approximately 9,000 years before European contact. Captain James Cook sailed through the passage between the islands on June 3, 1770, Whit Sunday in the church calendar, and named the passage accordingly. Whitehaven Beach on Whitsunday Island extends 7 kilometers and consists of 98 percent pure silica sand. The silica content creates sand that remains cool even in direct sunlight and produces a distinctive white appearance. Hill Inlet at the northern end of Whitehaven Beach contains tidal movements that shift sand and water, creating visible patterns that change with each tide cycle.
Port Phillip Bay forms a large enclosed bay south of Melbourne, covering approximately 1,930 square kilometers with an average depth of 8 meters. The bay connects to Bass Strait through a narrow channel called The Rip, which is 3 kilometers wide and experiences tidal flows exceeding 6 knots. Lieutenant John Murray sailed through The Rip in February 1802, becoming the first European to enter the bay. The Yarra River, flowing through Melbourne, enters the bay at its northern end. Approximately 4.5 million people live within the Port Phillip catchment area according to 2021 census data. The bay contains less than 3 percent of the marine biodiversity found in nearby Victorian coastal waters, likely due to its enclosed nature and limited water exchange, according to research published by the Victorian Environment Protection Authority.
The Kimberley coast in northwestern Australia extends approximately 12,000 kilometers when all islands and inlets are measured, despite the straight-line distance being roughly 1,000 kilometers. Tidal ranges in the Kimberley exceed 11 meters in some locations, among the highest in the world. The Horizontal Falls in Talbot Bay occur when tides force water through two narrow coastal gorges approximately 20 meters apart, creating a waterfall effect that reverses with each tide change. King George Falls in the Kimberley drops 80 meters directly into the ocean in twin cascades. The Mitchell Plateau coastline contains extensive reef systems, with some coral research suggesting these reefs may be more resilient to warming water temperatures than reefs further north.
The Tasman Sea lies between Australia's eastern coast and New Zealand, covering approximately 2,000,000 square kilometers. Dutch explorer Abel Tasman, sailing for the Dutch East India Company, became the first European to reach this sea in 1642. The East Australian Current flows southward along the coast, transporting warm water from the Coral Sea at speeds averaging 2 to 3 knots, with maximum speeds exceeding 7 knots. This current transports approximately 22 million cubic meters of water per second according to Commonwealth Scientific and Industrial Research Organisation measurements. Water temperatures in the current are typically 2 to 5°C warmer than surrounding waters. The current's influence extends the range of tropical marine species hundreds of kilometers south of their normal distribution.
Bass Strait contains significant oil and gas reserves, with production beginning at the Barracouta field in 1969. The Esso-BHP Gippsland Basin fields have produced more than 4 billion barrels of oil and 10 trillion cubic feet of gas since production began. The strait experiences rough sea conditions, with wave heights regularly exceeding 4 meters during winter months. The TSS Tasmanian Bridge ferry sank in Bass Strait on January 9, 1968, with no survivors among the 19 people aboard. Flinders Island and King Island are the largest of approximately 60 islands in the strait. Short-tailed shearwaters, also called muttonbirds, migrate approximately 15,000 kilometers annually from the Bering Sea to breeding colonies in Bass Strait, arriving in September and departing in April.
The Gulf of Carpentaria, bounded by Cape York Peninsula to the east and Arnhem Land to the west, covers approximately 300,000 square kilometers with an average depth of 69 meters. Dutch explorer Willem Janszoon in the Duyfken made the first documented European landing on the Australian continent at the Pennefather River on the western Cape York coast in 1606. The gulf experiences a tropical monsoonal climate with most rainfall occurring between December and March. Prawn fishing in the gulf began commercially in the 1960s, with the Northern Prawn Fishery now operating under strict quotas managed by the Australian Fisheries Management Authority. Approximately 20 rivers flow into the gulf, including the Roper River, Flinders River, and Norman River. Morning Glory clouds, roll clouds that can extend 1,000 kilometers in length, form predictably over the gulf between September and November.
Shark Bay in Western Australia covers 2.2 million hectares and was inscribed as a World Heritage Site in 1991. The bay contains the world's largest seagrass beds, covering approximately 4,000 square kilometers. These seagrass meadows support approximately 10,000 dugongs, about 10 percent of the world's population. Stromatolites, living structures formed by cyanobacteria identical to forms that existed 3.5 billion years ago, grow in Hamelin Pool at the southeastern corner of Shark Bay. Hypersalinity in Hamelin Pool, approximately twice normal ocean salinity due to restricted water circulation, creates conditions where stromatolites can survive despite being otherwise outcompeted by more complex organisms. The bay is named for the large shark population, with the Australian Institute of Marine Science estimating that Shark Bay contains one of the world's largest tiger shark populations.
The Coral Sea extends from the Great Barrier Reef east to Vanuatu and north to Papua New Guinea, covering approximately 4,791,000 square kilometers. Australia's Coral Sea Islands Territory comprises scattered reefs and islands east of the Great Barrier Reef. The Battle of the Coral Sea occurred from May 4 to 8, 1942, between American and Australian naval forces against the Imperial Japanese Navy. This was the first naval battle where opposing ships never came within sight of each other, with all attacks conducted by carrier-based aircraft. The Willis Islets in the Coral Sea contain Australia's only permanently staffed weather station in the territory, established in 1921. Water depth in the Coral Sea exceeds 4,000 meters in the abyssal plains.
The Indian Ocean coastline of Western Australia extends approximately 12,500 kilometers from the Kimberley to the Great Australian Bight. The Leeuwin Current flows southward along this coast, unlike most eastern boundary currents which flow toward the equator. This warm current allows tropical species to persist at higher latitudes than would otherwise be possible. The Margaret River region lies approximately 270 kilometers south of Perth where the continental shelf is narrow and the Leeuwin Current flows strongly. Perth experiences a Mediterranean climate unusual for western coasts at this latitude, partly influenced by the Leeuwin Current. The wreck of the Dutch ship Batavia lies in the Houtman Abrolhos Islands approximately 60 kilometers off the coast near Geraldton. The Batavia struck a reef on June 4, 1629, leading to a mutiny and massacre that killed approximately 125 people before rescue arrived.
Lake Eyre, known by its traditional name Kati Thanda, lies 15 meters below sea level in the central Australian desert. The lake covers approximately 9,500 square kilometers when full but remains dry most years. The lake filled significantly in 1974, 1984, 1989, 2010, and 2011. When full, the lake attracts large numbers of waterbirds, including pelicans that travel from coastal areas. The lake filled to approximately 25 percent capacity in 2019 following rainfall across the Lake Eyre Basin. Water in the lake is typically several times more saline than ocean water due to high evaporation rates. The lake sits at the lowest point of the internally draining Lake Eyre Basin, which covers 1,200,000 square kilometers, approximately one-sixth of the Australian continent. No water has ever reached the ocean from this basin in recorded history.
The coastline of Tasmania measures approximately 3,200 kilometers. The island's western coast faces the Southern Ocean with no land mass between Tasmania and South America. The Roaring Forties wind belt creates rough seas along this coast. Macquarie Harbour on the western coast has an entrance channel called Hell's Gates, approximately 100 meters wide, where tidal currents reach 3 meters per second. The Sarah Island penal settlement in Macquarie Harbour operated from 1822 to 1833, with approximately 1,100 convicts transported there during its operation. The eastern coast of Tasmania faces the Tasman Sea and experiences calmer conditions. The Freycinet Peninsula on the eastern coast contains Wineglass Bay, a curved beach approximately 600 meters long. Maria Island off the eastern coast served as a penal settlement from 1825 to 1832 and again from 1842 to 1850.
The Torres Strait Islands comprise 274 islands between Cape York and Papua New Guinea. Seventeen islands have permanent populations, with the total population across all islands approximately 4,500 according to 2021 census data. The Torres Strait Islander people are distinct from Aboriginal Australians, with a separate cultural and linguistic heritage. The strait was named after Spanish navigator Luis Váez de Torres, who sailed through it in 1606. The strait represents the drowned land bridge that connected Australia and New Guinea until approximately 8,000 years ago when post-glacial sea level rise separated them. Water depth in most of the strait is less than 15 meters. Thursday Island has been the administrative center of the Torres Strait since the 1870s and had a population of 2,610 in the 2021 census. Pearl diving in the Torres Strait began commercially in the 1860s, employing divers from various Pacific islands, Japan, and Malaya.
Botany Bay, located approximately 8 kilometers south of central Sydney, was the site of Captain James Cook's first landing on the eastern Australian coast on April 29, 1770. Cook's expedition remained at Botany Bay for eight days, with botanists Joseph Banks and Daniel Solander collecting numerous plant specimens. The First Fleet under Captain Arthur Phillip arrived at Botany Bay on January 18, 1788, but Phillip determined the location unsuitable for settlement due to poor soil and inadequate fresh water. The fleet moved north to Port Jackson on January 26. The Eora people inhabited the Botany Bay area for thousands of years before European arrival. Sydney Airport now occupies most of the northern shore of Botany Bay, with the international terminal extending on reclaimed land into the bay.
The Southern Ocean designation applies to waters south of 60°S latitude according to the International Hydrographic Organization definition adopted in 2000. Australian usage commonly extends the Southern Ocean designation to waters south of Australia regardless of latitude. The Antarctic Circumpolar Current flows clockwise around Antarctica through these waters, transporting approximately 135 million cubic meters of water per second, making it the largest ocean current by volume. This current effectively isolates Antarctic waters from warmer northern waters. Australian Antarctic Territory coastline extends approximately 5,900 kilometers, though territorial claims in Antarctica remain subject to the Antarctic Treaty System. Research stations operated by Australia in Antarctic territory include Mawson Station (established 1954), Davis Station (established 1957), and Casey Station (established 1969).