I was last there in late December. At that time, you could "legally" dive the small span by walking in from the boat ramp and swimming to the span. You had to park along the road and not in the park itself, however. Also, the park rangers wanted you to have a dive flag. Now, if you go on off hours, it is easy to hop the wall and go in from the south side of the small span which is what I've done the last couple of times.
Of note, I haven't seen seahorses there recently though others have. Most of the other life has returned since the 2004 hurricanes that decimated the area. I've recently seen lots of tropicals, eels, lobster, octobus, stingrays, horseshoe crabs, sea robins, a strange looking sea hare, and a southern stargazer. There is still one "wreck" under the bridge which has attracted some schooling fish.
I heard from one park ranger that they would be opening the park in January and that when it opened they would be taking down the gate from the south side opening. When that happens it should be back to Blue Heron Bridge diving as usual.
