Their is some diving out their best with a scooter. You have to watch the current carefully.
The Jetty is a good dive but can have some crazy current on it if the wind is blowing the wrong way on the south side. The north side is very current sensitive. You have to be mindful of hooks as their can be lots of fisherman. I did great with the spear gun out their on the submerged part. that is out their a long ways though 1.7 miles to the end of the submerged jetty.
as I said a scooter works great.
Half Moon bay is a shallow sand scape but I got my limit of crab the last time i was out their. It is protected but will get a rotor current going when in full tidal flow. If you learn the current and time it right you can make it do the work. again a scooter is best as it is a ways to get to deeper water.
Westhaven Point is okay, you can get crab it is mostly sand some rock here and their but you have to mind the current. Vis can be hell, high tide is the best.
The north jetty is great to dive I did some very nice drift dives on it allowing the current to carry me in then carry me back out again. Spear fishing was good. You have to mind the winds as the seas can come up. It is a half mile were the seawall is shear to the bottom. But getting out on the rocks of the seawall is a pain if the winds come up. if you drift to the end thier is usually a heavy rip on the north side of the jetty. Just go north to get out of it and you will get carried into shore. This is the surfing area on the north jetty.