Due to the absence of either natural lakes or rivers or groundwater in or near the city, a number of dams have been constructed on nearby creeks over the last 100 years to provide for the water needs of Bloomington and Monroe County. Early 20th-century damming projects occurred at locations southwest of the city, the most notable being the Leonard Springs Dam. Due to the limestone formations underlying the reservoirs and the dams, water kept seeping from the reservoirs through naturally developing underground channels. Despite all efforts, the city was never able to fully stop the leakage, and had to resort to pumping leaking water back to the reservoir.