I've always found fly fishing with any great success on this lake to be between May - August, but there are a couple of options (you will need be focusing on early morning or evening at this time of year) :
* Okere Falls above the control gates (slow sinking line, smelt or wooly bugger pattern) early morning, or below the control gates with a fast sinking line same flies (any time of day, but will be rafters around during the day).
* Hauparu Bay / Ruato Bay can still have a few fish around early morning, medium sinking line and smelt fly / wooly bugger for Hauparu, and floating / slow sinking line for Ruato.
* Possibly most productive option would be from the boat in the mornings and evenings around any drop-offs. Have had a bit of success at Hauparu Bay doing this in the mornings, anchor in the 4m depth on the edge of the drop-off and cast into the deeper water with a fast sinking line, it drops away quite quickly from 4m to 10m to 20m+. Fish will cruise those edges.
Was down over Labour Weekend and got most my fish jigging, about 6-7 nice fish all 4 - 6lb in good knick.
Best of luck!