As population continued to grow in the service area of USA, the water quality of the Tualatin River worsened. In 1986, the Northwest Environmental Defense Center filed a lawsuit against the United States Environmental Protection Agency, prompting Total maximum daily loads for the Tualatin River. A Clean Water Act amendment added regulation of storm-water runoff, and the Rock Creek Facility achieved 99% removal of ammonia nitrogen. In 1988, the Tualatin Valley Water Quality Endowment Fund was established by the Northwest Environmental Defense Center lawsuit.