June 2013: Freshwater and Altitude Diving, Lake Motosuko, Yamanashi, Japan

Saturday June 1st 2013


Lake Motosuko at the foot of Mt Fuji is a great introduction to freshwater and altitude diving.  Freshwater, or rather lakes, rivers and streams, offer some huge advantages such as excellent visibility and a range of things to see such as rock formations, stalagmites, mangroves and algae.  Freshwater is also less dense than salt water so less weight is needed, but add on altitude diving and there are various points to keep in mind.  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.

Every June, hoards of divers and non-divers descend on Lake Motosuko to participate in an annual cleanup 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. In the 9th century, Mt Fuji erupted and a large prehistoric lake separated into three smaller ones.  Lake Motosuko is one of the three.  

Before the clean up begins, 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 so my buddy and I swam westwards, descending slowly.  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 load becomes heavier.  

We swam past a slope of sediment and volcanic rocks at around 5m, strewn with items like fish hooks, fishing lines, beer cans, plastic containers, hair ties and small boxes that once contained takeaway meals.  Here we collected as much as we could before taking a slight right turn and swimming down to around 9-10m.  Near the lake are camp sites, excursion boats and windsurfing facilities so a lot of debris is simply dumped and pollution from various water activities has made the water quite cloudy so despite swimming carefully, visibility was not altogether great.  In terms of fish and plant life, we spotted a lot of weed-like plants and a couple of large grey fish, 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 extremely 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.

Not only does the cleanup 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 our group collected, once all the mesh bags were put together, has no doubt had some impact on Motosuko’s environment.

  • My dive group heads to Lake Motosuko on a Friday night and stays at one of the nearby camp sites for the weekend, ready to start our dive first thing on Saturday morning
  • Participation is arranged by our group and tanks are provided by the cleanup organizers.  Divers pay for their own transport to the area and camping facilities such as tent space, food and drink.  Those not keen to camp can also stay at one of the many cottages that are also part of the camp site.
  • For divers keen to arrange their own dives at the lake, the Motosuko Dive Resort, which charges around 12,600yen for 2 shore dives, might be a good option.  Their website is here: http://motosukodiving.com/

June’s dives

Dive 1: Lake Motosuko: depth: 9.4m, dive time: 29mins, water temp: 16C, entry time: 10:00AM, exit time: 10:29AM, average depth: 5.5m,used a 5mm wetsuit, 3mm hood/vest and 3kg weight (back plate as part of BC).  Saw plenty of weed-like plants and a couple of trout-like fish




1 thought on “June 2013: Freshwater and Altitude Diving, Lake Motosuko, Yamanashi, Japan

  1. Magnus

    Hee, I usually find the opposite to be true about freshwater diving. The visibility is usually worse, but maybe Swedish lakes are more nutrient dense than Japanese. Another thing I noticed is that the light tends to go to the green end of the spectrum rather than blue. Apparently you’re supposed to have a magenta filter rather than a red one if you’re taking pictures in such conditions.

    Also; 16 degrees is balmy, what are you talking about!? =P



Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s