Narrowsburg takes its name from a small, narrow rock canyon visible from the bridge, a passage only 200 feet wide that forms the narrowest point along the main stem of the Delaware River at river-mile 290 from the mouth of Delaware Bay. Local commerce was greatly enhanced by the accessibility of the interstate bridge, and the current bridge is the fifth erected at the narrows since 1810 after earlier covered bridges and a simple iron structure were washed away by floods. Just downstream lies the Big Eddy, the deepest place in the Delaware River, where a 113-foot-deep hole visible from the deck often has a whirlpool. This eddy is a quiet stretch of flat water bordered above and below by rapids, exposed rocks, and shallow water, and the deep hole is thought either to be a long-drowned plunge pool from a glacial waterfall or a pothole scoured by erosion, with smooth rocks at the bottom acting as the tools through tumbling action.