What I had always heard, and may be closer to the truth, was that it was parked there on the ice in the winter, because they wern't allowed to dispose of her, and needed to get it out of the way. The water evac training would be a classic military excuse to dump a plane in a lake though. 
Phil
Haha.
According to the report, the lake wasn't that full before. They used it for one year and the next year, after breakup, it filled up much further than it had been and remained at that height afterwards. In other words, they only got to use it for the training a couple times that same year.
As far as "getting it out of the way" this lake isn't exactly close to much of *anything* on post. They could have gone through much less effort and left it in the woods if they just wanted to move it.
IIRC report said that it was taken out of service initially awaiting parts. After that point it was damaged in a ground accident, it was deemed not salvagable (must have been some tug mishap!) so all usable parts were removed and it was designated to be scrapped before someone suggested water egress training.
