Marshall Lake, located in Boulder, Colorado, is a privately owned reservoir primarily used for irrigation purposes. Built in 1908, this Earth-type dam stands at a height of 80 feet and has a storage capacity of 12,878 acre-feet, making it a crucial resource for water supply in the region. The dam spans 2,370 feet in length and has a surface area of 305 acres, with a spillway width of 50 feet to manage excess water flow.

With its location along the South Boulder Creek, Marshall Lake plays a vital role in regulating water levels and ensuring a stable water supply for its surrounding areas. Despite being classified as having a high hazard potential, the dam is regularly inspected and maintained to meet regulatory standards, with its condition assessed as satisfactory during the most recent inspection in October 2020. The reservoir's risk assessment is rated as moderate, emphasizing the importance of continued risk management measures to safeguard against potential hazards and ensure the lake's long-term sustainability for irrigation and water supply purposes.