JEFFERSON CITY, Mo. -- A group representing state parks supporters sued Tuesday to stop the reconstruction of the Taum Sauk reservoir, two years after its collapse devastated a popular park.

The lawsuit by the Missouri Parks Association claims the Federal Energy Regulatory Commission failed to adequately study the environmental effect of reopening the hydroelectric plant or alternatives to rebuilding it.

It ask a federal court in Washington, D.C., to issue an injunction barring reconstruction of the reservoir until the federal agency prepares a more detailed environmental assessment.

Ameren Corp.'s mountaintop reservoir in Southeast Missouri failed Dec. 14, 2005, after the utility pumped too much water into the basin, causing it to overflow and ultimately erode and collapse the wall. The resulting torrent of water flooded nearby Johnson's Shut-Ins State Park and seriously injured the park superintendent's family.

Various state and federal investigations faulted Ameren for failing to repair inaccurate water gauges and for placing an emergency shut-off sensor so high on the reservoir wall that it was ineffective.

In 2006, Ameren agreed to pay $15 million in the largest-ever penalty assessed by FERC. The federal agency gave Ameren approval in August to rebuild the reservoir but required it to take various measures to reduce the effect of the construction on the environment and park patrons.

Two weeks ago, Ameren agreed to a nearly $180 million settlement with the state that also called for the reconstruction of the reservoir.

St. Louis-based Ameren already has selected a contractor to rebuild the reservoir.

The hydroelectric plant had been operating under a federal license that expires June 30, 2010. The lawsuit claims FERC should have treated the reconstruction approval as part of the licensing process and evaluated the environmental impact of both the construction and operation of the plant before approving its rebuilding.

Instead, the lawsuit says, FERC examined only the impact of the construction and the potential release of water from an overflow structure and is waiting to evaluate the reservoir's operating effect until the relicensure process.

"After FERC has authorized the expenditure of millions of millions of dollars to reconstruct Taum Sauk, there's not going to be a chance in a million that FERC is going to give this the unbiased evaluation it should get" during relicensure, said Bruce Morrison, an attorney for the St. Louis-based Great Rivers Environmental Law Center, which filed the lawsuit on behalf of the parks association.

The lawsuit says members of the not-for-profit parks group enjoy bird watching, hiking and nature study in the Taum Sauk area. They claim reconstruction of the reservoir would wreck the view of the mountain, reduce the water quality and quantity of a nearby river and creek and potentially effect a plant called "Mead's Milkweed," which is listed as a threatened species.