Just as u Drive over the Clarencetown bridge, on your right you'll see a camping ground. Drive down there, here u will park your car in shade, it's your launch point off the jetty, it also has toilets and water taps to hose off your board after your done. Keep in mind, you can camp here, if you want to explore it more. It's a very popular camping spot.
Once launched, turn to your right (away from the bridge which will be to your left)
Take the winding river down as far as you feel, and remember you will be heading upstream so on your way back should be easier going. Explore all the little side branches off the river that I like to call digon alley as they make great pictures.