Here's a good map of the Rapid River pools
Most everyone fishes between Middle Dam and Pond in the River
Below Lower Dam you get to stretch out, but it's a hike.
The upper gates are open at Upper Dam (between Mooselook and Upper Richardson) so the walk isn't too bad but expect to see a crowd.
What temps does the water need to get to to really triger the Brook Trout and Salmon to start the spawning run from the lakes ?
For the spawning run, it's not the water temperature that matters as much as the water level.
There has to be a "spate" of rain and rising water in order to get the fish to move into the rivers.
Some years that never happens before the end of the season. This year it poured like hell all the end of last week.
The sooner that you can get there after the water rises, the better off you are