I go over by boat and fish both Bellport and Old Inlet. Mostly slow, but can very occasionally explode with action. I was over at Bellport last Tuesday with my nephews. Rod was a half mile away in the boat. A school of blues came down the beach with a hurricane of birds over them. I ran to the boat, ran back, and managed a few 3lb blues while trying to catch my breath. No one else was fishing. That was a rare event, seeing the blues in the surf there in July. A few years ago during the fall season that area was great for weeks for both stripers and blues. Mostly its quiet though.
The dock at Old Inlet is maintained by the National Park Service, which administers the National Seashore. The stretch of Fire Island from Smith Point to Watch Hill is, I believe, the only federally-designated Wilderness Area in New York. Its full of wildlife, and there are also numerous freshwater springs. And ticks. Lots of ticks. Offices of the National Park Service are on River Avenue in Patchogue. There is no fee for tie up. As the previous post said, be careful going in at low tide.