This Altitude lake dive near Mt. Fuji is the site of an annual event that is a mix of camping and diving. Many who join will not dive and will enjoy the great views of Fuji and the lake/forest. The weekend experience: Fantastic…the diving…”less than fantastic”.
Motosuko is one of the “Fuji Go Ko” (Fuji 5 lakes) that were formed during various stages of volcanic activity from Fuji. Some of them are pretty deep, and due to this, Motosuko virtually never freezes over. I believe max depth for the lake is about 122 meters. There are stupendous views of Fuji from various points on the lake.
Being at 900 meters above sea level, the lake represents an altitude diving situation. This generally means diving to controlled depths (18 meters or less), reduced dive time (usually not a problem since it will be cold), and slower than normal ascents.
In the past, the water temps in June (month of the annual event) have been as low as 10 Celsius, but perhaps as high as 15 C. The bottom is generally mud and is easily disturbed by fin kicks are gathering activities, quickly eroding visibility. This is a good chance to practice frog kicking to reduce bottom disturbance.
Honestly, there is less to see compared to an ocean dive. The lake has populations of Trout, Bass and the smaller fish these predators eat. Some years, I have seen a lot of Bass (quite large at times) and sometimes they were aggressively protecting nests of visible eggs. However, other years I have seen no fish during my dive. There are interesting areas with petrified trees from when the lake formed.
Cleanup (June event)
There will be both in-water teams and shore patrols filling mesh bags with trash. Underwater, there is a mix of bento boxes, drink can’s/bottles and fishing lures/gear. Careful, as there can be a lot of lures/lines with hooks. There can also be larger debris (ties, boat parts, etc.) which we will not attempt to lift.