Foul Rift is an approximately quarter-mile long stretch of Class II rapids in the Delaware River, locate about a mile south of Belvidere, New Jersey. The rapids are caused by a descent in the elevation of the riverbed, and are considered by locals to be the most dangerous on the Delaware River, though the actual difficulty of navigating this stretch of the river is greatly exaggerated. However, at higher water levels some of the narrower rapids can become extremely dangerous.
Foul Rift is one of four rapids on the Delaware River. The other three are the Skinners Falls Rapids south of Hancock, New York; the Mongaup Rapids where the Mongaup River empties into the Delaware north of Hawk's Nest, New York; and the Port Jervis rapids just north of Port Jervis, New York. All four rapids are considered Class II on the international scale, however in very high water, they become Class III.