I believe I mentioned about this before, but as it still goes unfixed, Ahti is the god of waters, not forests. Also he (obviously) isn't Tapio's wife, but Mielikki is and SHE's the goddess of forest.
Yes, I have received dozens of emails about this (and also about Satan being listed as feminine). I've not had time to fix it yet, but sometime this fall I'll be doing an update. Mike