As with The Outland Count's task You don't need to actually go out and find the headwaters if you already know the co-ordinates. To find them yourself simply follow the River north until you reach a point where you can "check". As with before you will be prompted to mark the location and report back. For those too lazy for the leisurely flight up the river, or you are still having trouble finding the exact location, the co-ordinates are A/1-2/2.