The Glenmaggie Dam is a concrete block-foundation gravity dam with 14 radial arm gates across the Macalister River, located near Maffra, Central Gippsland, in the Australian state of Victoria. The dam's purpose includes irrigation, the generation of hydro-electric power, water supply and conservation. The impounded reservoir is called Lake Glenmaggie.

Construction of the Glenmaggie Dam commenced in 1919, was completed in 1927 and constructed by the State Rivers and Water Supply Commission of Victoria. When full following its construction, the dam held 132,000 ML (4,700 million cu ft) and provided irrigation to approximately 360 square kilometres (140 sq mi) of farming land in the Central Gippsland region; via a gravity irrigation systems to properties in the Macalister Irrigation District, near the towns of Maffra, Heyfield, Stratford and Sale. The Macalister Irrigation District covers about 53,000 ha (130,000 acres) around the Macalister and Thomson rivers, extending from Lake Glenmaggie to Sale. It comprises two areas: the Maffra-Sale Irrigation Area to the north of the Thomson River and the Central Gippsland Area (including the Nambrok-Denison Soldier Settlement district) to the south.

The Glenmaggie Dam wall, which creates the Glenmaggie Lake, is a mass concrete overfall dam with irrigation outlets on both sides of the river serving irrigation channels. The central portion is an overfall spillway. The dam wall was raised in 1958 by the addition of gates; stabilised using ground anchors in 1989; and upgraded in 2003 to enable it to withstand overtopping.

In 1994, a hydro-electric power station with two Francis turbine-generators was commissioned, with a capacity of 4 megawatts (5,400 hp) and generating 9 gigawatt-hours (32 TJ) per annum.

In June 2007, the Macalister catchment experienced record flooding. Inflows into Lake Glenmaggie peaked in excess of 250,000 ML (55 billion imp gal; 66 billion US gal) per day and releases peaked at 147,000 ML (32 billion imp gal; 39 billion US gal) per day. A second flood occurred in November 2007 with inflows into Lake Glenmaggie peaking at 70,000 ML (15 billion imp gal; 18 billion US gal) per day and releases peaking at 59,000 ML (13 billion imp gal; 16 billion US gal) per day. Repairs totaling around A$4 million were completed after the June and November 2007 floods.

There is a local legend that the lake is haunted by a ghost by the name of Matilda Power who died in an unfortunate accident back in 1939. It's rumoured that her ghost roams the shores to this day looking for her car that was lost in over 14 feet of water. Local ghost hunters say that she's often spotted by the lake at the end of Gillum Road, particularly in March each year.

• Irrigation in Australia
• List of dams and reservoirs in Victoria