WASHINGTON (AP) _ The state of Missouri and the U.S. Army Corps of Engineers have spent years tussling over water policy on the Missouri River. Now they are fighting over dirt.

Corps officials want to dredge about 23 miles of side channels and then dump up to 24 million tons of the soil into the river to help create a better habitat for endangered fish.

But Missouri's Clean Water Commission says all that sediment contains high levels of nitrogen and phosphorous that cause pollution.

"In our state, we spend $40 million a year to keep soil out of our rivers," said Kristin Perry, who heads commission.

The state agency's objections forced the corps to halt work on two dredging projects last summer, one at Jameson Island near Booneville and another at Rush Bottom, north of Kansas City.

An order from the commission on March 12 continued the prohibition on soil dumping, causing the corps to cancel at least three other dredging projects in Missouri.

For the corps, the standoff is delaying its mission to comply with a federal mandate to improve conditions for the pallid sturgeon, a fish on the endangered species list that once thrived before upstream dams changed the flow and soil composition of the river, often called the Big Muddy.

"It's called the Big Muddy, but it's only got one-third of the sediment it used to have," said Mike George, manager of the corps' Missouri River recovery program. "That's got a lot of impact on wildlife. We're just taking where the river used to run and trying to make it run a little bit there now."

The new side channels allow some of the river water to travel more slowly and at shallower depth to provide more favorable fish habitats. Channels are designed so that further erosion will occur over time, the way river erosion used to occur naturally.

Perry says her commission is simply enforcing federal and state anti-pollution laws like the Clean Water Act, which prohibit farmers from dumping excess soil into the river.

For years, government scientists have blamed pollution from farm fertilizer, soil erosion and sewage treatment plants for the "dead zone" in the northern Gulf of Mexico. The oxygen-depleted area has grown as pollution is carried downstream from the Missouri and Mississippi rivers.

"Ultimately what's driving this is a fundamental fairness argument," Perry said. "We're trying very hard to keep nutrients out of the water and paying money to do that while at the same time our government is dumping it in."

Mike Wells, deputy director of the Missouri Department of Natural Resources, has been working with the corps and the state to reach a compromise. He said the state is finding it difficult to balance the mandates of different federal agencies.

"There's two federal laws out there that appear to be in conflict," Wells said. "In this case, it would mean complying with the Endangered Species Act versus complying with the Clean Water Act."

To help resolve the dispute, the corps this month asked the National Academy of Sciences to examine whether sediment dumped into the Missouri River reduces water quality and leads to low oxygen, or hypoxia, in the Gulf of Mexico. The study is expected to take about two years.

Meanwhile, the corps will cease dredging operations in Missouri and focus habitat restoration efforts in Kansas, Nebraska and Iowa, where states have expressed no objections.

"We've really tried to work through this government to government so that we don't have to end up in court," said George, the corps official.

Copyright 2008 The Associated Press.