Catalina Cove can be nice for snorkeling, but visibility varies and it can get very crowded. A better spot that is very nearby is off of Arashi beach, just north of Catalina Cove (very hard to miss- there is a big parking lot right off of the road). At Arashi beach, there is a very nice shallow reef (5' to 15') on the far right side of the beach. It is a bit tricky to find- you do need to swim out a ways to find it. But once you find it, it's a great spot.