From the end of the old road climb below Carn na Nathrach but stay above the forest. When you get to Allt Coire na Creadha follow the burn down to the forest road which will take you to the A87. No path but no problems.

I went this way in the bad weather last year, and once you get to the point where the old A road reaches the North side, it is perfectly possible just to make your way clockwise round the lochside edge itself. I recommend however that if coming from the west, you ascend up to the old A road as soon as it comes in view (I didn't - and regretted it!)