Environmentalists have filed a notice of intent to sue the owners and operators of a massive hog farm in eastern North Carolina for illegally discharging animal waste that's fouling the Trent River.

The Neuse Riverkeeper Foundation and the Waterkeeper Alliance aim to stop pollution from Stilley Farms, which confines more than 11,000 hogs near Trenton, N.C. The farm -- what's known as a "concentrated animal feeding operation" or CAFO -- raises the swine for Murphy-Brown LLC, the livestock production subsidiary of Virginia-based Smithfield Foods, the largest U.S. pork producer and processor. Smithfield was purchased by the Chinese pork giant Shuanghui International Holdings in September 2013.

The groups plan to file suit under citizen enforcement provisions of the federal Clean Water Act and Solid Waste Disposal Act if action isn't taken to stop the discharges and clean up the facility within 90 days.

"Corporations that now control the meat production industry are threatening public health," said Robert F. Kennedy Jr., president of Waterkeeper Alliance. "Since the government is looking the other way, we are taking action to compel this industry to comply with federal law and stop using North Carolina's waterways for disposal of swine waste."

Hog waste contains pathogens, nitrogen, phosphorus, and other pollutants that can cause fish kills, endanger swimmers, promote toxic algae blooms, and contaminate drinking water. The Stilley Facility is discharging the pollution into tributaries of the Trent River, which flows into the Neuse Estuary, an important fishery that regularly experiences pollution-related algae blooms and fish kills.

The N.C. Department of Environment and Natural Resources has acknowledged that its efforts to reduce pollution for nearly two decades have failed to achieve "any significant decrease in actual nutrient loading to the estuary" and that phosphorus pollution of the Trent River has actually increased.

The environmental groups threatening to sue point out that NCDENR often claims that animal feeding operations in the Neuse Basin operate under "no-discharge" permits. Yet the agency admits that the operations often directly discharge swine waste to public waters through ditches and drains -- a violation of both state and federal law.

"The continued mismanagement of swine waste at Stilley Facility is a danger to the health of North Carolinians and the environment," said Larry Baldwin, CAFO coordinator at Waterkeeper Alliance. "The communities that depend on clean, healthy water from the Trent River and the greater Neuse River basin have a right to clean water and, since the government hasn't taken action to address this issue, we will."