Lower Long Lake, also known as Long Lake No 2 or Campbell Reservoir, is a public utility water supply located in Arvada, Colorado. This earth dam structure, completed in 1939, stands at 19 feet tall and spans 1350 feet in length, with a storage capacity of 409 acre-feet. The reservoir serves as a critical resource for water supply in the region, with a normal storage capacity of 292 acre-feet and a maximum discharge of 330 cubic feet per second.

Despite its importance, Lower Long Lake poses a high hazard potential and has been assessed as unsatisfactory in condition, with a moderate risk level. The dam is regulated by the Colorado Division of Water Resources, which oversees permitting, inspection, and enforcement activities to ensure the safety and integrity of the structure. With its location on Ralston Creek, Lower Long Lake plays a crucial role in water management and climate resilience efforts in Jefferson County, Colorado. Water resource and climate enthusiasts will find this reservoir a key focal point for understanding the intersection of infrastructure, sustainability, and environmental stewardship in the region.