Sydney has quite a few deep water wrecks at the depth of 45-50 metres. One of those wrecks is the Coolooli a popular wreck with Sydney Divers. And the Valiant one of the few shallower wrecks at 26 metres. The visability on these wrecks are usually 5 to 10 metres and sometimes in winter when the winds are blowing offshore it has been reported as being 30 metres.
The Coolooli is a bucket dredge and was one of 10 ships skuttled off Long Reef in 1980 to form an artificial reef. The wreck is easily penetrated but I recommend you don't on your first dive and only if your experienced with deep water wrecks. The Coolooli is an amazing dive during the day and I have dived it at night which was quite errie. The wreck lies on its side in the sand and the buckets are clearly visible.
Picture Gallery - Diving on Sydney Wrecks