South of Perth off Warnbro Sound, the snorkeling in the Shoalwater Island Marine Park is a popular destination known for bottlenose dolphins, stingrays and sharks. Off the rocky limestone shores, there are cavernous reefs providing habitat to a range of marine life. The best snorkeling dive sites are the shore-accessed Cape Peron and the boat-accessed site called The Sisters.
Two of the more popular sites to visit include Seal Island and Penguin Island. Both are habitat for seals, which you must stay at least 10m away, and the later is known as habitat for the largest breeding colony of Little Penguin. Penguin Island is closed from June thru September.
Some of the Shoalwater Island Marine Park snorkeling dive sites are accessible via ferry from Mersey Point or from Rockingham.
Overall, Shoalwater Island Marine Park is the 18th most popular snorkel dive spot of all 24 snorkeling dives in Western Australia.