Valley Lake sits inside one of the volcanic craters on the rim of the Mount Gambier maar complex, just south-west of the Blue Lake. The lake and the surrounding wetlands form a wildlife sanctuary that attracts large numbers of waterbirds — pelicans, herons, cormorants, and black swans are regulars. The area has been managed as a sanctuary since the 1880s and is one of the most accessible urban wildlife reserves in South Australia.
A walking trail loops around the lake, passing through stands of native vegetation and offering views across the water and towards the volcanic rim. The crater walls rise steeply on all sides, giving the site an enclosed, otherworldly quality. Koalas are sometimes seen in the eucalypts around the lake's edge.
The Boandik name for the lake is Ketla Malpi. The site is free to enter and can be reached from the Blue Lake precinct in about a fifteen-minute walk, making a natural circuit of both crater lakes.