Can you swim at Lake Kussharo?

I know there are open-air onsens but I am having difficulty verifying if people are allowed to actually swim in the lake.

While Lake Kussharo is vast, the area known as the Wakoto Peninsula offers the easiest access to the water; details can be found on the website of the Ministry of the Environment's Hokkaido Regional Office, which manages the site. The following link points to a Google-translated English version of the original Japanese page:

https://hokkaido-env-go-jp.translate.goog/blog/page_00258.html?_x_tr_s...

Simply put, entering the water is not prohibited. This differs significantly from places like the Azusa River in Kamikochi, where entering the water is banned (due to environmental protection concerns and the dangers posed by low temperatures and swift currents). In summer, the water temperature reaches around 22–24��C; while cold, it is not impossible to enter. On sunny days, the temperature in the shallows might rise slightly higher.

However, I believe that swimming out toward the middle of the lake and back—even if not explicitly forbidden—is something one should avoid. Such activities do not contribute to the local community, and an accident would cause significant trouble for the locals. It is best to limit yourself to swimming near the shore in water no deeper than waist-level (and only in good weather).

If you wish to support the local economy, I recommend joining a SUP or canoe tour. Although the aforementioned webpage advises wearing a life jacket, I was unable to find any places offering life jacket rentals. Naturally, life jackets are provided during SUP and other tours, so that is not an issue.

You can find various companies by searching for "Lake Kussharo nature tours."

Of course, this applies to the summer season; you should not swim during the colder months.

Not specific to Lake Kussharo, but something that came up earlier this year. I had some guests that wanted to do some ocean swimming and of course, swimming beaches are more geared towards summer and July-onwards with some facilities not being open outside of that "season".
Regarding Frog's mention of cold, it does depend on the person. When my group did go swimming (well, half of them), water temperature would have been around 14��C. They said it was fine.

When i was in Okinawa between 16.06-23.06 - then i also wondered why there seem so few locals on the beaches. I have never been on Maldives but based on photos - the beaches in Okinawa prefecture (i was only in Zamami and Azama Sun beach) provide quite good competition. Furuzamami beach had maybe only 20 persons in water and on Azama Sun beach i was the only one who was in areas where depth is more than 2 meters. Is it due the school system? I learned from my exchange student that in Japan the summer holiday for students is much shorter compared to Estonia or rest of the Europe. Of course i tried to be more cautious due the fact that you never know when you have earthquake and after that a tsunami so probably i was not as relaxed as in Greece or Croatia.

BR,
Lauri

While looking at this again, I did find a link saying - yes, you can go swimming. https://www.visit-hokkaido.jp/en/ has a page for the lake.
@Lauri - I do think it is linked to the summer holidays and I have seen this in a few places. When I was living in west Tokyo I would regularly go past a water park in July when temperatures were well into the 30's, but the place remained closed until the school break later in the month, not because it wasn't hot, just they probably would not have had the numbers to make it commercially viable.
Similarly, visiting Shimoda/Shirahama Beach a few years back in June was really cheap because it was "pre-summer" as far as they were concerned. (And, there was not much open around the beach area.) The city website currently states the beach will open July 18th, although when I was there a group of dedicated surfers were making the most of the small waves available.
It could also be linked to water temperatures as you know Japan heats its hotels, trains and other places a lot and avoiding cold situations. As Frog mentioned 22-24C is cold to him. When I was growing up my local pool was usually around 20C and my Irish guests said anything over 10C would be fine. But when I visited Ireland last year, their 28C heatwave was a cool respite for me after the 38C of Tokyo.

International Ranking of the Percentage of People Who Can Swim

https://honkawa2.sakura.ne.jp/3620.html#google_vignette

Nordic countries have high rates of people who can swim (with many exceeding 90%). Australia (88.0%) and New Zealand (84.7%) also show high figures. Japan ranks 39th globally at 62.5%—lower than its soccer ranking—though it does beat Brazil. It is surprising that the figure is this low, given that most public elementary and junior high schools have pools and conduct swimming lessons. Since Japanese people are generally considered to have low self-assessment, this trait might be reflected here as well (as these figures are based on self-assessment).

There is a common rumor that fishermen in Hokkaido—particularly in the northern and eastern regions where the fishing industry thrives—cannot swim. The prevailing explanation is that because the ocean water is cold, the ability to swim is not considered a significant issue.

It is now common knowledge that locals in Okinawa do not swim in the ocean. There are both historical reasons and ongoing issues behind this. Historically, the adoption rate of swimming pools in Okinawan elementary and junior high schools was low in the past, meaning many people above a certain age never learned to swim. Then there are the dangers of the sea. One major risk involves dangerous marine life, particularly jellyfish. While designated swimming beaches in Okinawa usually have jellyfish-prevention nets, the risk of encountering jellyfish increases outside these areas. Even if the water looks beautiful, one might still get stung if there is no net. Another factor is ocean currents; depending on the topography, strong currents can pose a risk of being swept away, leading to swimming bans in certain areas—Kabira Bay on Ishigaki Island is a famous example. Finally, there is the issue of ultraviolet (UV) radiation. UV levels in Okinawa are said to be roughly double those in Tokyo, making sunburn a significant concern. In recent decades, tanning has increasingly been viewed as harmful due to links with cancer and other health issues, so it has become common practice to wear clothing while entering the water. I recently saw news of the "sea opening" (the start of the swimming season), and more than half of the people—mostly children—were wearing clothes. If a foreign visitor to Japan comes across a swimming beach—and you can generally assume that any spot where locals are entering the water is a designated swimming area—and decides to go in, it is perfectly acceptable to enter the water in everyday clothes rather than a swimsuit. The only real point of etiquette is to ensure you are wearing clean undergarments. I haven't swum in the ocean myself for about twenty years, but back when I did, I used to swim usually with shorts and a T-shirt.

Access to the ocean is generally unrestricted; there is no nationwide ban on access. However, local governments or smaller community groups may sometimes prohibit access for various reasons, such as safety hazards or environmental concerns. It is best to comply with such restrictions.

This is heading off topic, but some additional context to @Frog's post. For New Zealand and Australia, the bulk of the population live near the coast and access to ocean swiming or pools is relatively high. When I was in elementary school, learning to swim was part of the school day during summer, but when my daugher was a similar age, it was private swimming lessons instead of school taught, so there was a shift in approach across time. Pretty much everyone got taught how to swim, and then they didn't. Another contributing factor to the decline in swimming rates might be the change in population mix. NZ/Aus have growing asian populations and unfortunately (based on media reports), they appear to have a lower level of ability and do get into trouble on some of the beaches around NZ.
On the UV side of things, my daughter liked her "rash" tops - looks like a t-shirt, but designed to screen out the UV. Swimming in a cotton t-shirt isn't too sensible unless you're just splashing around IMO.

Yes, you can swim at Lake Kussharo. We were there in late June and I swam a few times, although I didn't see anyone else in the water.

Our Airbnb host said that although swimming is allowed, June is considered too cold.

The water temperature was 16ºC, which as a Brit I didn't find bad, especially as you can warm up in a hot spring afterwards.

I thought the beach next to Wakoto Hot Spring was the best for swimming. I preferred the hot spring at Ikeno-yu, but the lake was shallow there and a bit hard to swim in.

Water shoes are useful as the lake is rocky.