A federal agency has approved a plan by Denver's water utility to raise the height of an existing Colorado dam by 131 feet (40 meters) and nearly triple the amount of water it stores.
The Army Corps of Engineers announced late Friday it granted the project a permit under the federal Clean Water Act.
The $380 million project involves Gross Dam in the foothills about 5 miles southwest of Boulder.
The project still needs approval from the Federal Energy Regulatory Commission to increase the dam's hydropower capacity.
Denver Water wants to raise the dam to 471 feet (144 meters). That would expand the reservoir from 42,000 acre-feet (52 million cubic meters) to 119,000 (147 million cubic meters). One acre-foot (1,200 cubic meters) can supply two typical households for a year.