Low Water at Grant "Lake" Reservoir In normal and wet years, Grant "Lake" Reservoir fills this entire basin but not so in the last three years. The Wold War II era dam for this reservoir was designed with one purpose only: to store as much water as possible for the Los Angeles Department of Water and Power. Newer dams allow water to be released downstream to maintain healthier ecosystems and a recent landmark agreement between the Mono Lake Committee and the LADWP will modernize the antiquated dam in the next four years.