Close up photo of the dam at Lake Murray Reservoir. The City of San Diego took over operation of the Lake Murray Reservoir in 1950 from the Helix Irrigation District, then purchased the reservoir from Helix 10 years later. It is located within the boundary of the City's Mission Trails Regional Park. When full, the reservoir has 171.1 surface acres, a maximum water depth of 95 feet, and 3.2 shoreline miles.