That fisherman I talked to said the reason why the oxygen got law was the lake froze over early and had snow cover for a very long time. This prevented the plants in the lake from making oxygen, hence the very low levels. Normally this lake doesn't have a problem with winterkill since it has a good amount of water 15 - 20 ft. deep and even as deep as 25 ft. in places.
At this point I'm just happy to report the only casualties I saw were the trout and one fairly large catfish.