The highlighted (black line) on the attached map is a slight variation of the Butlers Gorge - Lake King William Ride that I got sent this week which allows you to avoid the climb up the hill back under the powerline just south of Derwent Bridge.  

Here's the full details I got sent:
"The water level was about 7 metres below full and an old ford was visible where you can see the track crossing to the western band. Water was below knee deep but a few larger stones in the bottom were slippery. (Was able to ride half way across before losing it).
"Was a much better option than back up the hill under power line. The lake shore around to the ford was quite rideable with only a couple of short spots where we had to get off the bike.
"The water level at the ford is easy to check out before starting the ride, can drive there. Not sure how much the lake would have to rise to flood it."