Snorkeling Catalina Cove is pretty good with many fish, a smattering of corals and a good number of sponges to see on the various sized boulders. It can be accessed either by shore or boat tour. Unless you don't have a rental car, or you really want the Aruba boat tour experience, we recommend snorkeling this spot from shore.
Snorkeling Boca Catalina, which is the beach just to the left of the cove, has an easier water entrance. But there simply isn't much of anything to see. It has a sandy bottom with some seaweed patches. You have to swim over to the cove and past it to see much of interest.
The water entrance closest to the good snorkeling area is in Catalina Cove. It is rocky with some sand, but doable with some footwear. If there are any waves, don't attempt this entrance because you could easily lose your balance around the rocks.
If it is too wavy or you have no shoes, enter instead in the sand at Boca Catalina (the farthest sandy beach in the picture below). Walk to the left of the cove until you reach the sandy beach and enter there.
If you have shoes, consider doing a one-way drift snorkel entering at Catalina Cove and exiting at Arashi Beach. Then make the short walk back on the road to your car at Catalina Cove.
If you enter in the cove, you can swim a little to the left and check out the small rocky point there. If you enter from the sand, swim to the right seeing the same area.
Then, swim out and to the right around the rocky point. Don't stay too close to shore as it gets too shallow. But, you can range a good ways away from shore as it stays shallow enough for snorkeling. You will see boulders of many sizes with a few corals, many sponges and a good number of fish. You will likely encounter a group of fish looking for a handout. It is obvious that the snorkeling Catalina Cove tour boats feed the fish here.
The depths in the area range from about 2 to 5 feet. Unfortunately we had terrible visibility when we snorkeled here. There was an algae bloom and the water was simply fuzzy with it and it covered the bottom too. We hope you have better water clarity.
There were absolutely millions of silversides and large schools of juvenile grunts.
There are a couple of shade palapas on the beach. There are more on Boca Catalina too.