Maintaining Transparency
Lake Shikotsu is famous as a beautiful, deep blue caldera lake. It is also well-known for having the cleanest, clearest water in Japan—so much so that the town works hard to keep hotels, restaurants, and other facilities from polluting the lake. For example, the public sewer that serves the local hot spring has been redirected so as not to damage these pristine waters. One reason for this clarity is the lack of plankton, algae, or other living material. The area around Lake Shikotsu is still sparsely developed so there is little human detritus, one of the biggest causes of water turbidity, and the operation of motorboats, jet skis, or other motorized vehicles on the lake is forbidden.
Just how clear is this water? Measurements taken in 2002 found one spot that was clear to an unbelievable depth of over 30 meters. However, the average “transparency depth” is now estimated to be between 15 and 20 meters, a remarkable achievement for any body of water. Of course, locals swear that the water used to be even clearer fifty years ago, but current tests are enough to assure any visitor that this is the clearest water in Japan.