Adriatic sea is amazingly clean and blue, it is the best for snorkeling. The only problem is that there are not many animals to sea close to the beach. People can go snorkeling themselve or, i havent tried it, but there is a company Butterfly Diving, which arranges trips by boat around Tucepi (Hvar, Brac, Podgoda, Baska Voda). The instructors lead you and show you how to dive if you dont have any experience yet. The trips are for the whole day. I dont know the price.