I was just up that way.
It's generally agreed that trout fishing in southern and western Maine rivers in August has the same problems as Pennsylvania- low, warm water. This year has been a good one- wetter than usual. But many of the rivers are still only borderline- about 70 degree temps. And frankly, Pa. has many more cold running brooks and headwater wild trout streams than southern Maine.
I crossed over the Wild R. in Bethel about a week ago- it was very low. The wild fish in there tend to run pretty small, too. It gets some supplemental stocking.
My guess is that the Wild got blown out from the heavy rains in the area a couple of days ago. It's a steep gradient river that tends to alternate between flash flooding and a trickle. Gorgeous place- I've camped and fished there, up around Hastings. But my experience is that the fish are only fingerling size.
In my opinion, it's worth it to head farther north, past the Rapid (which is too warm this time of year) to the lower Magalloway- a bottom release tailwater where the water temps are always in the 60s. I was there in mid-July- plenty of trout in the river.
These guys know the deal http://www.rangeleysportshop.com/blog/
If you can hold out until September, trout opportunities expand considerably in the southern and western part of the state. Serious fish. Spawning runs, etc.