The Rocklands Reservoir, a water reservoir, is created by a major ungated concrete-walled gravity dam with embankment sections across the Glenelg River in the Wimmera region of Victoria, Australia. It is the largest reservoir within the Grampians–Wimmera–Mallee Water (GWMWater) supply system. Originally constructed to supply the Wimmera-Mallee Domestic and Stock channel system, water held by Rocklands Reservoir is now used for many different purposes. A unique feature of Rocklands Reservoir is that all entitlement holders, including the environment, are able to be supplied with water from the reservoir.

Construction of the dam began in 1938. World War II caused construction to cease, and it was recommenced in 1950, with the dam being completed in 1953. Its catchment area is 1,355 square kilometres (523 sq mi).

A 270-metre-long (890 ft) cement gravity dam forms the main wall, and is flanked by two embankment sections. At 100% operating capacity, the dam wall holds back 261,510 ML (9.235 billion cu ft) of water. The reservoir is capable of holding up to 348,300 ML (12.30 billion cu ft) of water. At 100% capacity, the surface area of the reservoir is 67.5 square kilometres (26.1 sq mi). The spillway is capable of discharging 763 cubic metres per second (26,900 cu ft/s).

Rocklands Reservoir is a popular recreational boating location, with powerboating, water skiing and jet skiing allowed. Camping is permitted in designated areas. During the duck hunting season, duck shooting is allowed. It is also a popular fishing spot, with Murray cod, redfin, trout and carp taken at all times of the year. Rocklands had a reputation as one of the premier carp fishing destinations in the late 1990s and early 2000s with ten-plus-kilogram carp taken regularly.