Amid one of the hottest summers on record for Colorado, Dillon Reservoir is 94% full, nearly 5 feet below its capacity. The reason is a complex combination of past weather patterns, current water-use habits and recent changes to the lakebed.
For most of the summer, Dillon Reservoir has been down about 4 1/2 feet. This low elevation is noticeable from the shore, but the drop in water level is less pronounced than it has been in other dry years. Around this time in 2018, Dillon Reservoir’s elevation was dropping an inch daily and was down about 11 feet by Labor Day.
Dillon Reservoir is no normal mountain lake. The man-made reservoir is one of the largest sources of drinking water for Denver. Usually in late June, Denver Water holds back water that flows into Dillon Reservoir from the Blue River basin and stores the water until it’s needed along the Front Range. In late summer, Denver Water typically begins piping water out of Dillon Reservoir via the Roberts Tunnel, a 23-mile pipe that runs under the Continental Divide and into the North Fork of the South Platte River. From there, the water flows down toward Strontia Springs Reservoir, where it’s delivered to Denver Water’s customers.
In most normal water years, managers at Denver Water are able to fill the reservoir to its 257,000 acre-foot capacity in the spring, and recreation along the reservoir is usually best when it’s full. This year, unseasonably warm spring weather created dry soil that absorbed much of the moisture from melting snow before it reached rivers. Wind and low precipitation in May also contributed to a lackluster runoff season. Denver Water was able to fill Dillon Reservoir to 244,000 acre-feet of water, about 95% of its capacity. The reservoir levels have hovered around that number ever since late June.
“You know, 95% seems like it would be pretty full, but in the past, at this point, we would be moving docks and boat ramps would be unusable,” Frisco Bay Marina General Manager Tom Hogeman said. “But other than tightening cables on docks to adjust for different water levels, we haven’t had to move anything.”
