Lake Motosuko: Freshwater Diving and An Underwater CleanUp

Hundreds of years agolava flows dammed up rivers as a result of multiple eruptions from Mount Fuji, creating 5 lakes that today make up a region known as the Fuji Five Lakes, or in Japanese Fujigoko. At 1,000 meters or so above sea level, Fujigoko is one of the best places for close-up views of Japan's highest and most famous mountain.  Hiking, camping, fishing and snow sports are among the popular outdoor activities that can be enjoyed, while there are plenty of hot springs and museums for those who prefer something less strenuous.  For diving, it's not exactly well known butone of the lakes in the region, Lake Motosuko, is famous for an event that takes place each year.

In early June, hoards of divers and non-divers arrive for an annual clean-up project aimed at removing debris and litter from the lake bottom and surrounding areas.  The lake is around 900 meters in altitude and goes down to a depth of around 138m.  Following a Mount Fuji eruption in the 9th century, a large prehistoric lake separated into three smaller ones that are still connected with each other by underground waterways.  LakeMotosuko is one of the three.

Before the clean up, divers can pick up a map from the organizers, which marks out areas with the most litter.  Once separated into pairs, they are then free to choose where they want to go and head right in.  The lake is caked in thick sediment (ash and silt) so stable buoyancy is crucial.  Kicking hard will stir up the sediment and worsen visibility, making things difficult not just for yourself but also for your buddy and in the worst case you can lose each other altogether.  Each buddy pair also has a mesh bag to put the litter into so the diver with the bag must remain suitably buoyant as his or her load becomes heavier.  

Upon descent, the underwater scenery begins with a slope of sediment and volcanic rocks, strewn with items like fish hooks, fishing lines, beer cans, plastic containers, hair ties and small boxes that once contained takeaway meals.  Usually the clean up is conducted at a maximum depth of around 9-10 metres.   A lot of debris is simply dumped into Lake Motosuko due to the camp sites, excursion boats and windsurfing facilities that are close by, while pollution from various water activities has made the lake cloudy so despite swimming carefully, visibility is not altogether great.  However, there is some life to be spotted such as weed-like plants and some large grey fish that are probably a type of trout, as rainbow and brown trout are known to inhabit the lake in addition to shrimp and other smaller fish.  At 16 degrees the water is cold.  Wearing a dry suit is the best option by far but it’s possible to cope in a 5-7mm wetsuit and a 3mm hood and vest underneath.  A hood and gloves are also essential.  Due to the altitude and low temperature, 30 minutes is the recommended time to stay underwater.

Lake Motosuko is a great introduction to freshwater and altitude diving.  Freshwater, or rather lakes, rivers and streams, offer some huge advantages like decent visibility and a range of things to see such as rock formations, stalagmites, mangroves and algae.  But add on the altitude and there are various points to keep in mind while diving.  The reduced atmospheric pressure at the surface affects depth gauges and when the diver ascends, the rate of change as the ambient pressure drops is far greater than when ascending from a dive in the sea.  Adjusting your dive computer to the equivalent setting is a must.

Not only does the clean-up help the community of Motosuko and the environment, but it also provides an opportunity for divers to experience something new and practice their skills, buoyancy in particular or even areas such as searching and retrieving.  In other words it’s a great opportunity to help out and gain some expertise.  The amount of litter collected, once all the mesh bags are put together, no doubt has some impact on Motosuko’s environment.

Discovery Divers Tokyo  takes part in the Lake Motosuko clean up each year. Check out their website or Facebook page for more information.  For divers keen to arrange their own dives at the lake, Motosuko Dive Resort charges around 12,600yen for 2 shore dives, or fun dives can be arranged through Discovery Divers Tokyo.