The inside of the north jetty is a demanding dive. The currents are very strong and the main channel for large boats through the inlet runs very close to a considerable length of that jetty, so you really have to hug the rock pile. There are major siltation problems in the center and south part of the inlet, especially at the point it enters Barnegat Bay, so boats coming into and leaving the bay tend to travel very near the north jetty. The Manasquan inlet is easier, and Shark River inlet is a piece of cake in comparison.
During the summer the boat traffic is incredibly heavy, so you really have to stay right in against the rocks. The jetty continuues for a long distance beyond the inlet, much of it completely underwater, and some decent diving can be found on the outside the jetty well beyond the inlet's mouth, especially on the outside part of the north jetty, where a kind of cove is formed in the right angle between the rocks and the beach. A beach entry is possible, though you need a 4 wheel drive to get there. There is a tremendous variety of marine life to be seen everywhere in the inlet, from big striped bass and lobsters to an amazing variety of Caribbean tropicals during late summer.
Water clarity is often a problem, since dredging operation are continuous, and powerful currents keep things in suspension. I dive the inlet, especially the inner parts of the north jetty where it enters the bay. In summer, when the winds are from the north there are days when huge lenses of Gulf Stream water move in, bringing crystal clear water and tropical sea creatures. Pelicans are always present during the warmer months, and the sight of dozens of Butterfly fish on every boulder can make you think you are in the Caribbean.
Recently the state and Feds began letting small groups of divers dive the wonderful south jetty near the lighthouse. There is a Coast Guard station there, and they can provide information. All inlet diving is, of course, limited to the half hour before and the half hour after peak high tide. The currents are utterly impossible other times. I've been diving that inlet for decades, and it helps to know exactly where and when to go. It's not everyone's cup of tea. You have to be VERY careful. There are many fisherman, sometimes hostile, and a rats nest of fishing line and tackle everywhere, so a good knife and shears is important. Night diving at peak high, especially after Labor Day can be wonderful when water conditions are right.
