Mystical Lake Mashu in Hokkaido is swathed in mist for more than 100 days of the year. Hemmed in by steep mountains and with no river flowing into it, it is known for its exceptionally clear water. This lake, however, is in crisis. Its water clarity, once the highest in the world at 41.6m, has dropped year by year. Trees in the surrounding mountains have started to wither. What is going on at Lake Mashu? A survey team set out to discover the cause of the lake's deterioration. Could it be mudslides? Or the soaring deer population? Various possibilities were considered but... Science View hunts down the real culprit. Tune in for the must-see conclusion!