Sydney’s coastline boasts many spots for good snorkeling. There are protected bays and reserves like the Cabbage Tree Bay and Bronte Coogee Aquatic reserves which are sanctuaries for marine life. While inside the harbour, the Sydney Harbour National Park has its own unique marine life.
During the Sydney Summer, bathers will be fine. But in Spring, Winter and Autumn months you will need a wetsuit.
Snorkel tours by local operators are an option. You can learn more about Sydney’s marine ecosystem and they will provide full gear hire and transport.