I am a marine biologist and work at a public aquarium in California. About a week ago on my day off I was freediving with my buddy at Catalina Island. When I glanced back at our boat right after leaving it, I saw a very large Great White Shark tracking me from behind. The shark made a 8 foot pass and moved on. I yelled to all the divers in the area to stay out of the water and we all exited. We swam back to the boat and waited for a while and saw a sea lion come in and it wasn't bothered. We waited about an hour or so and went back in thinking that the shark had moved on. About five minutes into the dive I was on the surface and it came out of no where right at me and then veered away, it was about 3 feet from me at this time. I estimated the shark to be approximately 14 feet or bigger. Later a tuna spotting plane said they also saw a 14 foot shark around Avalon Banks a few hours before I saw this one, it could have very well been the same shark.