For the best snorkeling, skip Isla de Roqueta and go straight to Puerto Marques. When you enter town and get to the restaurants, go left. Drive all the way to the end of the bay. The guys there will watch your car and your stuff should be safe – we didn’t have any problems. Pay when you leave. There are beach tables and umbrellas to rent for $3. They serve great food.
On the far left side, you can snorkel the entire length of the cove. We went out six or seven football fields. There’s good visibility and, unlike what we saw at Roqueta, there was no trash in the water. The farther out you went, the bigger the fish got with more variety. The water was calm each time. We bring our own gear and snorkel right off the beach. Don't waste your money on a snorkel cruise in Acapulco. They have lots of shops there where you can buy or rent gear, but we've found out over the years just to get your own gear that fits and you'll always have a better experience.