The passage of the Clean Water Act in 1972 signaled the beginning of US efforts to improve the quality of its waterways. The act imposed stricter controls on point source discharges into rivers and other navigable waters. This eventually led to the installation of three wastewater treatment plants on the banks of the Concord River: one in Concord and two in Billerica. These plants have helped to prevent subsequent damage to the river ecosystem when they were able to operate within federally mandated limits.