IMAX movies in kelp beds are usually shot at San Clemente Island.
Pyramid Cove has lots of favorite spots.
More info here.
But there aren't many trips because of the distance. The 5 to 6 hour trip, each way, isn't good if you get seasick easily. You board late at night and find a bunk below. The engines start around 1 AM, and you arrive at the island around sun-up. Dive until noon-ish, then back in the harbor around an hour before sunset. It's easier on the body on a multi-day trip. The military sometimes shuts down areas for various reasons, and that can impact boat schedules. San Clement hints at what Catalina used to be like way back in the 1950's, so I've been told (I'm not THAT old!).
One dive became memorable just after I surfaced, about 100 yards abeam from the boat. I noticed a HUGE gray fin coming straight at me, from what looked like just 100-feet away. I had game on my stringer - it's the only time I've been truly scared diving - suspecting the fin belonged to a great white. What other fin is that big and doesn't arc when it moves, as dolphins and whales swim? I knew I couldn't out-swim a GW, so I just kept facing the looming fin. A small kelp mat blocked my underwater view of the fish. I unhooked my stringer, ready to give up my catch. As that big fin kept getting bigger, my spear gun felt inconsequential. The fin started listing to one side(?), not straight up and down. Then the silhouette of the fish turned sideways, and 1/2 the body was "missing." Phew. Mola-molas (sunfish) grow much bigger than this...
They're VERY curious animals...
...get really huge...
...and sometimes like playing scare-the-diver peek-a-boo through kelp @ San Clemente...