The O'Shannassy River is a tributary of the Yarra River

Yarra River

The Yarra River, originally Birrarung, is a river in east-central Victoria, Australia. The lower stretches of the river is where the city of Melbourne was established in 1835 and today Greater Melbourne dominates and influences the landscape of its lower reaches...

. It rises on the southern slopes of the Great Dividing Range

Great Dividing Range

The Great Dividing Range, or the Eastern Highlands, is Australia's most substantial mountain range and the third longest in the world. The range stretches more than 3,500 km from Dauan Island off the northeastern tip of Queensland, running the entire length of the eastern coastline through...

, around 80 km East of Melbourne

Melbourne

Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...

, Victoria

Victoria (Australia)

Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....

, Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

. It is dammed by the O'Shannassy Reservoir

O'Shannassy Reservoir

The O'Shannassy Reservoir is located on the O'Shannassy River - a tributary of the Yarra River - near McMahons Creek, around 80 km East of Melbourne, Victoria, Australia. The reservoir is part of Melbourne's water supply system...

, which forms part of Melbourne's water supply system.
The O’Shannassy River catchment is identified as an Essentially Natural Catchment by the Land Conservation Council.
The river is named after John O'Shanassy

John O'Shanassy

Sir John O'Shanassy, KCMG , Australian colonial politician, was the 2nd Premier of Victoria. O'Shanassy was born near Thurles in County Tipperary, Ireland, the son of a surveyor, and came to the Port Phillip District in 1839...

 (sic), 2nd Premier of Victoria.