Cotter Dam, Gravity and embankment dam in Australian Capital Territory, Australia

Cotter Dam is a water storage dam in the Australian Capital Territory that combines a concrete gravity section with a rockfill embankment across the Cotter River. The reservoir it creates supplies drinking water to the Canberra region.

Work on the dam started in 1912, shortly after Canberra was chosen as the new capital, and the original structure was finished in 1915. About a century later, a major upgrade completed in 2013 significantly raised the dam wall and expanded the reservoir's capacity.

Garrett Cotter, an early settler in the area, gave his name to both the river and the dam. The reservoir water is pumped to Mount Stromlo and then flows by gravity into Canberra's reservoirs. The dam precinct received a Historic Engineering Marker from Engineers Australia.

The area around the dam is open to visitors and the drive there passes through open bush country. Conditions on unpaved sections can change with the weather, so arriving on a dry day makes the trip easier.

The 2013 upgrade included the creation of a fish habitat stretching about 7 kilometers along the river, put in place to protect the rare Macquarie Perch. That same project made the dam the largest roller-compacted concrete structure of its kind in Australia.