A watershed group is seeking national recognition of Virginia's Mattaponi River as an "endangered" waterway because of a 6-mile-long, 13-billion-gallon reservoir that has been proposed in the York River Tributary.

The Mattaponi and Pamunkey Rivers Association recently announced that it would make the nomination to American Rivers, a national conservation group which annually produces a highly publicized list of what it considers to be the 20 most threatened U.S. waterways. The Newport News Waterworks is seeking to build a $120 million reservoir on Cohoke Creek, a Mattaponi tributary, to help meet the needs of the Williamsburg-Hampton-Newport News area through 2040. "We find this proposal both implausible and completely unnecessary," said Billy Mills, executive director of the Mattaponi and Pamunkey Rivers Association, one of several groups fighting the reservoir plan. "The multiple serious environmental impacts ... pose a grave danger to all of the dependent living resources of the Mattaponi River system and ecology."

He said he hoped that seeking the"endangered" status for the Mattaponi would help focus regional and national attention on the river, which meets the Pamunkey to form the York River.

The reservoir proposal has drawn strong opposition from environmental groups who charge that the Newport News region is trying to grab water from distant watersheds to fuel sprawl development far into the future.

Waterworks officials have said that an adequate water supply will help concentrate development in areas that have existing infrastructure. Up to 75 million gallons a day could be drawn from the reservoir.

The Virginia chapter of the Sierra Club in late summer released a report saying the demand for water would be only be 15 million to 20 million gallons per day, significantly less than previously estimated. The group said that meant other alternatives could meet regional water demands, such as building a second brackish water desalination plant in 2020 to supplement one already being built.

David Morris, planning and programs director for the waterworks, disputed that demand for water had been overestimated. "I'm still very comfortable with our numbers," he said.

The Mattaponi remains relatively undeveloped and has been studied as a potential scenic river by the National Park Service. The project would flood 524 acres of wetlands and 1,457 acres of forests. Opponents object to the out-of-basin transfer of water, and say it could draw salt water farther up the Mattaponi, affecting aquatic ecosystems.

To proceed, the project needs both state and federal approval. Both the State Water Control Board and the U.S. Army Corps of Engineers have taken comments on the proposal, but neither have set a date for ruling on the permit. The U.S. Fish & Wildlife Service has opposed the project, and the EPA has asked for more information about its potential impact.

- The Associated Press contributed to this report