Mary’s Lake is located in an enlarged natural basic several miles south of downtown Estes Park. It is part of the Colorado-Big Thompson Project power system. Mary’s Lake serves two primary purposes: it acts as an afterbay for the Mary’s Lake Power Plant, and it helps regulate C-BT Project water on its way to the Estes Power Plant.
As water exists the Adams Tunnel’s East Portal, it drops 205 feet through a large penstock to the Mary’s Lake Power Plant. The Prospect Mountain Conduit and Tunnel carries water from Mary’s Lake to the Estes Power Plant penstock.
Mary’s Lake and its dikes cost $410,000 to build.
Mary’s Lake has a capacity of 927 acre-feet, 42 surface acres, 1 mile of shoreline and a maximum depth of 33 feet.