I was in sydney for 3 weeks and only surfed. Be sure to get a tour of Kings Cross on a fri or sat night, otherwise Manly beach is pretty chill.
I got a pull on an inlet in 03. Down in wollongong. South of the city shark nets. Kinda freeky if you havnt been exposed to the ocean or brackish water. Bull sharks = no good.
I fell and the spotter was watching something else, left me about a 1/4 mile back. i felt like bait in dark water.
I lived in perth for a bit and they had a man made lake ski competition type setup. not sure about the syd scene though as I didnt spend much time there. Should be able to find a Moomba to drag you around the sydney waterways.