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Some of the most unusual species in Australia live in the fast-flowing waters of the Eastern Australia Rivers and Streams ecoregion. Many are endemic, and some have survived here for millions of years. A long series of plateaus and high mountains known as the Great Divide borders the east coast of the continent. The Divide is the major source of the rivers and streams in this ecoregion. Some of these waterways run for short distances toward the sea, while others flow inland to distant parts of Australia. This ecoregion also includes the rivers and streams of Tasmania, a small island off of the coast of southeastern continental Australia. This island receives abundant rainfall compared to much of the mainland.
From the Great Divide flows the Darling River, which feeds into the Murray River. These rivers are two of Australia's largest. At the southern end of the Divide lies the Snowy Mountain range, which has the highest peaks in Australia. Farther to the north, smaller rivers and streams are home to species that have been around since Australia was part of the Gondwanaland "supercontinent" 200 million years ago. Southeast Australia is home to many species of fish and crayfish, a large proportion of which are endemic. Ancient aquatic species live here, too, such as lungfish, dragonflies, mountain shrimp, and mayflies. Endemic fish include the Murray jollytail, the primitive spotted bonytongue, and the migratory Australian grayling, which may be the only living member of its genus and is considered vulnerable. Tasmania has a large number of endemic fish of its own, including the Shannon paragalaxias and Tasmanian whitebait. The Murray River crayfish has big white claws, grows to be over 14 inches (35 cm) in length and can weigh up to 6 pounds (2.7 kg)! Australia's largest freshwater fish, the Murray cod, grows to more than 5 feet (1.5 m) long. A large number of freshwater snails have highly localized distributions within portions of the ecoregion. And the most famous of all freshwater species in eastern Australia, the duck-billed platypus, digs long tunnels and deep caves in riverbanks.
There are many threats to freshwater biodiversity here. Rivers and streams have been highly modified by the construction of weirs and dams, by channelization, and by the removal of riparian vegetation. Agricultural, urban, and industrial pollution are growing problems in some areas. Introduced species, including fish and aquatic plants, threaten natives. These exotics include species brought from other Australian regions. Aquaculture threatens to further the spread of non-native species, as well as to release wastewater into freshwater ecosystems. The clearing of forests for agriculture and timber production, and subsequent increases in sedimentation, may be one of the most serious problems.
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