MILWAUKEE (AP) — A federal judge in Wisconsin has ordered NCR Corp. and Appleton Papers Inc. to pay an estimated $700 million to clean a contaminated river, the latest effort to hold paper makers accountable for toxins in the Green Bay waterway.

NCR, based in Atlanta, and Appleton, based in the Wisconsin city of the same name, must share responsibility for cleaning up the most contaminated segment of the Fox River, U.S. District Judge William Griesbach ruled Monday.

The channel is polluted with toxic chemicals called PCBs, which are used in the paper-making process. NCR dumped PCBs into the river between 1954 and 1971 as a byproduct of carbonless paper production, but argued in court it wasn't the only company to do so.

NCR and Appleton had asked the court to have other former and current paper companies share in cleanup costs. Instead, Griesbach ruled NCR and Appleton must bear the cost themselves and reimburse other companies for any future cleanup costs.

Griesbach said NCR was the only company that knowingly discharged PCBs, and said other paper companies that recycled NCR products didn't realize the waste they were dumping contained the toxins.

The explanation didn't placate Katherine Querard, an Appleton spokeswoman who said other companies that caused damage also should be liable.

"We are more than willing to pay for our fair share, but we are equally adamant that others should also pay for the damage they caused," she said Thursday.

NCR spokeswoman Anne Marie Agnelli said the company was assessing the ruling's significance but didn't expect the impact to be material. She declined to elaborate.

The ruling didn't hamper NCR's shares, which rose 27 cents, or 1.4 percent, to close Thursday at $19.33. Appleton is privately owned by employees.

The state of Wisconsin and the U.S. both still have claims against NCR, Appleton and a slew of other paper makers.

Griesbach's ruling came in a summary judgment, meaning there was no trial. Querard called it "baffling" that the judge could issue a ruling that way, without giving the company a chance to fully state its case in a trial.

Production of PCBs was banned in 1979 after the chemicals were shown to cause cancer in wildlife and be a likely carcinogen for humans.

The cleanup project involves dredging the PCB-contaminated sediment on the bottom of the river and shipping it to a processing facility for treatment, before it is sent to a landfill. Water is cleaned and returned to the river. In other areas, sediment will be capped and covered on the bottom of the river to hold PCBs in place.

The goal is to lower the level of the pollutants, and therefore health risks, for boaters and others exposed to the water, humans who eat fish, and fishing-eating birds and mammals.

The cleanup overseen by the U.S. Environmental Protection Agency involves a 13-mile span of the river in northeastern Wisconsin, the largest environmental remediation project of its kind. The project started in 2009 and is expected to last until 2018.