Mountaintop mining and extraction of natural gas from the Marcellus Shale have placed two West Virginia rivers, the Gauley and the Monongahela, on the 2010 list of most endangered rivers.

The nonprofit American Rivers prepares the list of rivers threatened by pending decisions each year. The list based on nominations from river groups and concerned citizens across the U.S.

Rivers are chosen for most endangered status based not on current stresses, but on pending permitting, regulatory or other actions that could significantly impact their health.

The Gauley River is listed as No. 3 in 2010 because of to mountaintop mining.

Citing effects including burial of streams, contamination of drinking water, displacement of communities and increased flooding, the organization has called on the U.S. Environmental Protection Agency to protect water quality by creating national standards for conductivity and selenium in streams.

Appearing as No. 9 is the Monongahela River in West Virginia and Pennsylvania.

Troubling the Mon River, the organization's report states, are the combined effects of old and current coal mines as well as the beginnings of natural gas extraction from the Marcellus Shale.

In 2008, gas well hydraulic fracturing fluids that were high in dissolved solids fouled drinking water for Mon River communities in Pennsylvania. Municipalities at the time accepted gas well wastewater they could not adequately treat. While they have discontinued the practice, neither West Virginia nor Pennsylvania has yet passed water quality standards for dissolved solids.

In 2009, drainage from coal mines, also high in dissolved solids, contributed to a fish kill on the Mon River tributary Dunkard Creek.

The organization calls for the enactment of water quality standards for dissolved solids -- a process that already is under way in both states.

American Rivers also called on Congress to pass the FRAC Act to repeal the exemption for gas well fracturing fluids in the Safe Drinking Water Act and to require disclosure of the chemicals used in those fluids.

The last time a West Virginia river appeared on the list was in 2006. That year, the Shenandoah River was listed for poorly managed development.

Topping the list this year is the Upper Delaware River in Pennsylvania and New York, which provides drinking water to 17 million. American Rivers said that river also needs protection from improperly treated Marcellus Shale fracturing fluids.

Rounding out the list are the Sacramento-San Joaquin River Delta in California, threatened by outdated water and flood management; the Little River in North Carolina, where better alternatives to a proposed dam may be available; Iowa's Cedar River, subject to outdated flood management; the Upper Colorado River in Colorado, depleted by excessive water diversions; the Chetco River in Oregon, threatened by gravel mining; the Teton River in Idaho, also threatened by a new dam; and the Coosa River in Alabama, where the renewal of seven hydropower licenses pose an opportunity for increased protections for endangered species.

This is the 25th year American Rivers has highlighted the nation's most endangered rivers. The group said its advocacy efforts have helped to improve rivers throughout the United States, including the removal of old dams and prevention of new ones, restrictions on mining and oil and gas drilling, and policy revisions that stopped the draining of wetlands.