The federal Environmental Protection Agency is ordering 13 Inland Empire dairies to clean up their act.
Federal regulators say the Chino area dairies have not taken adequate steps to prevent manure and other pollutants from flowing into tributaries of the Santa Ana River.
The dairies, says the EPA, have failed to take what it calls reasonable action to minimize discharges, put in place proper waste management plans and conduct routine inspections that could prevent contaminants from running into nearby creeks and streams.
Requests by the EPA follow about six months after Santa Ana Regional Water Quality Control Board inspectors discovered the alleged violations. These inspections take place during rainy months when contamination problems are most visible.
EPA officials say the dairies contacted this week are among dozens inspected between November 2010 and February 2011.
The federal agency delivered a similar warning to one of the dairies three years ago. The EPA's Regional Administrator for the Pacific Southwest says the agency is evaluating whether it will impose fines on all or some of the dairies. A worker at one of the dairies told the San Bernardino Sun newspaper that it could cost tens of thousands of dollars to make the upgrades and avoid future penalties.
Dairy owners contacted by the EPA have until Dec. 31 to make improvements.
If dairies fail to comply, new orders can be issued, fines up to $37,500 a day can be levied and civil lawsuits can be filed.
Michael Marsh of Western United Dairymen in Modesto says none of those cited were members, but he notes last winter brought record rain to the whole state.
The Associated Press contributed to this report.