HAGERSTOWN, Md. -- The Nature Conservancy said yesterday it has created an advisory committee to help evaluate stream pollution from dirt and gravel roads in western Maryland and southwest Pennsylvania.

The project is aimed at providing local officials with data about erosion and sediment runoff in three Potomac River tributaries -- Fifteen Mile, Sideling Hill and Town creeks -- said Donnelle Keech, director of the organization's Allegany Forests Project.

She said sediment, much of it from dirt and gravel roads, is the most pervasive threat to the streams.

The Nature Conservancy said it will hire a contractor to drive all the dirt and gravel roads in the area and gather data on their condition.

Some of the problems could be addressed by rebuilding eroded stream banks near roads, redirecting eroding culverts or planting vegetation along roads to reduce erosion, spokesman David Dadurka said.

The Nature Conservancy is a private, nonprofit conservation group based in Arlington, Va.