American Rivers

Two polluted tributaries of the Chesapeake Bay, one urban and the other rural, rank among the most threatened rivers in North America, a national conservation group said yesterday.Runoff from Washington-area streets fouls the Anacostia River, and pollution from Pennsylvania farms has put the Susquehanna at risk, said American Rivers, a Washington-based organization.The Anacostia, which flows from Maryland through Washington, and the Susquehanna, the bay's largest freshwater artery, made the group's list of 25 waterways considered "in serious decline."