The Glenelg River, a perennial river of the Glenelg Hopkins catchment, is located in the Australian states of Victoria and South Australia.
The river rises in the Grampian Ranges and flows generally north, then west, then south, for over 350 kilometres (220 mi), making the river the longest river in south-west Victoria and third longest overall. A short stretch of the lower end winds through southeastern South Australia before returning to Victoria to enter Discovery Bay at Nelson. The Glenelg River is a central feature of the Lower Glenelg National Park.
The river was named after Colonial Secretary Baron Glenelg, Charles Grant, by Major Thomas Mitchell in August 1836.
Large amounts of water diverted from the upper reaches of the river for agricultural purposes, including irrigation and town water demands. The estuary is listed under the Heritage Rivers Act, 1992 (VIC) and is a nationally important wetland.
The Glenelg was important to Indigenous Australians. It formed the traditional tribal boundaries for the nomadic Bungandidj people (western bank) and Gunditjmara people (eastern bank) people from two distinct language groups. Little archeological evidence has been found of Bunganditj in-habitation along the river itself, including in the regions many caves, there is strong evidence of their presence in nearby coastal areas. While strong evidence of Gunditjmara activity has been found along the river's eastern hinterland and shell middens discovered may indicate multiple nomadic tribes camping along the river that may have used message sticks to communicate. It is not known how long indigenous Australians had been associated with the river, however it is estimated to have been many thousands of years.