Natural resource extraction in large undeveloped areas-such as the Bristol Bay watershed in Southwest Alaska-often necessitates construction of roads that contribute substantial environmental risks. Herein, we attempt to address risks from a proposed mine transportation corridor in a virtually roadless watershed that crosses important salmon streams and rivers. The Bristol Bay watershed supports the largest sockeye salmon fishery in the world. A proposed 138 km permanent access road would connect a porphyry copper/gold deposit to a deep-water port. Of 64 potential stream crossings, salmonid spawning migrations may be impeded by culverts at 36 crossings, 32 of which contain restricted upstream habitat. After cessation of mine operations, assuming typical maintenance practices, 10 or more of the 32 streams with restricted upstream habitat would likely be entirely or partly blocked at any time. Consequently, salmon passage-and ultimately production-would be reduced in these streams, and they would likely not be able to support long-term populations of resident species. Additional long-term risks associated with operation of the road include filling or alteration of National Wetland Inventory aquatic habitats; spills of highly toxic xanthate or cyanide due to truck accidents; and reduced habitat quality due to dust production from traffic. We discuss our methodology, and information needs, in the context of Environmental Impact Statements that set the stage for decisions regarding future mining projects.