Both the dam and river are named after early settler in the area Garrett Cotter.
The impounded Cotter Reservoir is a supply source of potable water for the city of Canberra and its environs.
The original concrete gravity Cotter Dam was designed by Harry Gustav Connell (The Department of Home Affairs supervising engineer in Canberra from 1912 to 1916).
However, in December 2004, ACTEW Corporation brought the dam back on line in response to the ongoing drought.
Completion was originally scheduled for the end of June 2011,[4] however construction was delayed until August 2013[5] due to heavy rainfalls in the summer of 2010/2011,[6] the discovery of an unexpectedly large rock seam at the site of the foundations in 2011,[7] and severe flooding in March 2012.