I've filmed at the Tangalooma wrecks on Moreton Island off the Brisbane coast. It's a magical site (and relatively safe) to snorkel and swim around. The wrecks are close to the main beach and the water is always clear and a magnificent blue colour with an abundance of marine life. It's truly spectacular.
As it's within the confines of being part of a National Park, the Government has done a superb job in clearing out most of the obstructions making this a very safe area to dive, snorkel and swim in.