Tonnes of diving.
Water temp in April is about 20-22 degrees metric.
Pro Dive, Sydney Dive Charters you can just book and turn up to the dive site/boat ramp, they'll have all the equipment there and ready.
Dive Centre Manly, Dive Centre Bondi you'll meet at the shop and they'll take you to the dive site.
Other dive shops will want you to pick up gear including tanks from the shop first then head to the site/wharf. I mention this because it can be problematic if you don't have your own transport. Maybe you can bum a lift off someone else headed to the site, but I tend not to rely on that.