A federal judge says pumping water from farmlands into public water supplies such as Florida's Lake Okeechobee violates the Clean Water Act.
Environmental groups say Friday's ruling by U.S. District Judge Kenneth Karas in New York's Southern District was "long overdue."
The nonprofit environmental law firm Earthjustice first filed its case in 2002 over polluted water from sugar cane and vegetable fields pumped into Lake Okeechobee.
Earthjustice argued that the South Florida Water Management District violated federal law by allowing agricultural companies to send polluted water into southern Florida's water supply without decontaminating it first.
The Florida case was bundled with similar claims from several other states and heard in New York federal court.
Environmental groups say stopping pollution at its source is key to fixing South Florida's water problems.