Near Denville in northern New Jersey, the Rockaway River has about 30 miles of productive fly-fishing and is reasonably close to New York City.
The best stretch to explore is from Wharton to Dover. The river is accessed by SR699, SR46 and SR15. You will want to make sure to stay above the Jersey City Reservoir, below which is not known to be a good tailwater fishery.
There is a good shore access point for flyfishing on the Rockaway River right in Dover at the Dover Waterworks. You can enter off Rutgers Street from Princeton Avenue, and there is plenty of good parking.
Overall, Rockaway River is the 7th most popular fly fishing river of all 10 fly fishing spots in New Jersey.