O'Shannassy Reservoir

O’Shannassy Reservoir is filled by rainfall received by the surrounding catchments. It supplies water to Silvan Reservoir, which distributes it to most parts of Melbourne.

When the reservoir overflows, water spills into the Yarra River. Some of this water can be pumped back out into Sugarloaf Reservoir.

Key facts

The dam at O’Shannassy Reservoir is an earthfill embankment with reinforced concrete core wall, and was completed in 1928.

Aerial image of O’Shannassy Reservoir

  • Catchment area: 11,900 hectares
  • Surface area: 27 hectares
  • Total capacity: 3,123 megalitres
  • Dam height: 34 metres
  • Dam length: 226 metres
     

Rainfall over the years

View highlights from our historical rainfall data for O’Shannassy Reservoir, including annual rainfall, monthly averages, and the wettest and driest years by month.

Live rainfall and water storage data

Get the latest information on each of our 10 major reservoirs, including daily water storage levels and hourly rainfall and river level data.

Annual rainfall at O’Shannassy (1927-2021)

Graph of annual rainfall (mm) at O'Shannassy Reservoir, 1927-2021

Monthly rainfall records (mm)

Last updated: January 2022

Month Wettest Driest Average
​January 174.2 (1956) 1.8 (1990) 65.7
February​ 246.4 (1939) 0.4 (1991) 62.7
March​ 189.0 (1970) 3.6 (1951) 71.7
April​ 295.7 (1935) 13.2 (1963) 102.2
May​ 364.2 (1960) 3.0 (1934) 125.2
June​ 438.4 (1952) 23.0 (2006) 134.9
July​ 310.4 (1964) 45.0 (1994) 148.2
August​ 433.1 (1939) 49.8 (1982) 170.8
September​ 280.8 (1992) 34.0 (1961) 149.0
October​ 315.5 (1934) 22.4  (2015) 132.6
November​ 252.5 (1952) 25.9 (1927) 110.5
December​ 231.6 (1930) 9.4 (1972) 96.3
Annual total 2166.9 (1952) 829.4 (2006) 1369.9
Last updated:
28 January 2022