Harriman Reservoir in Littleton, Colorado, was built in 1873, making it one of Denver Water's oldest reservoirs. Denver Water owns the reservoir, dam and land within the park, while Foothills Park & Recreation District manages the recreation at Harriman Lake Park.

The reservoir delivers irrigation water to Fort Logan National Cemetery, Jeffco Public Schools, Pinehurst Country Club and other nearby areas.

From December 2011 to February 2013, Denver Water replaced the then-138-year-old dam with a new earthen dam to satisfy regulatory requirements and bring it to its full capacity for storage.