Actually the shore-accessible reefs are excellent from about Hallandale to Pompano. We dove Hollywood (s. of Dania Beach) yesterday and it was awesome.
You could actually SCUBA within Pennekamp Park but you won't see much. I used to take my mask and fins there in my bicycle basket so that I could swim laps with fins to build endurance. The water within Pennekamp is shockingly cold so if you are trying to SCUBA dive it, take a wetsuit...and be prepared to see very little.
On the other hand...I highly recommend putting on an exposure suit, leaving the tanks in the car, and snorkeling along the mangroves within Pennekamp. It's a couple of inches deep and teeming with life. It's where the juvies live when they are growing up, you will see adorable two inch long baraccuda for instance. I've taken friends to do that many times and they have had manatees come up to them.