Open Water Swimming in Japan

Very little information is written about the sport of OWS in Japan in English (plenty in Japanese though). I will attempt here to make available in English, information about Open Water Swimming in Japan. Open Water Swimming in Japan is governed by the Japan International Open Water Swimming Association (JIOWSA).

What is Open Water Swimming?

Open water swimming is any distance of swimming that takes place outside of a swimming pool. Most open water swim events take place in the ocean (beach/surf swim), lakes, rivers, but can include bodies of waters such as bays, harbours and channels. The mission of JIOWSA according to their website is: “Our Mission is to deliver their health and safety to any open water swimmer; to consider the nature in harmony through open water swim events.” Open Water Swimming is an activity for all ages and abilities. It’s a great way to explore beaches of Japan and cool yourself in the incredibly hot summers of Japan. There are approximately 30 OWS events held throughout Japan from Okinawa to Hokkaido during the summer months. The OWS season begins in May and continues to October, with the bulk of the events in June, July and August.

The most important information for OWS in Japan can be found on the following sites: JIOWSA – information on OWS, the governing body in Japan, and a list of only JIOWSA OWS events and results. Open Water Swim JP (now defunct) – contains a very comprehensive list of OWS events regardless of whether they are JIOWSA events or not.
This is my preferred go-to website for all OWS events, however has not been updated in the last few years. SportsEntry – this is the site that you will be directed to 90% of the time if you plan on putting an entry in for any OWS event. They too list the majority of OWS events in Japan, and it is the centralized registration (and payment) site for most of the events.

This blog – As all of the above info is all in Japanese, this blog is gonna be your best bet to keep updated on OWS info and events in English. I will do my best to translate as much info as possible into English. Various smaller private communities, sporting organisations and other NPOs also host open water swim events. As of 2012, I’ve noticed a new organization that has popped up and is hosting a handful of OWS events. NOWS – National Open Water Swimming Japan. Website here.

Please feel free to contact me if you need help reading/translating information from Japanese regarding open water swimming in Japan. Take a read of some of my race reports in the race results/write-up page to get a better feel of open water swimming in Japan. Lots of pics available.

2018 Japan Open Water swimming calendar

(Current as at 16 March 2018)

April OWS

April 8 Hota OWS Time Trial 1.5km/3.8km Chiba prefecture Entry:



May 12 9th Annual Manazuru Iwa kaigan OWS 1km/2km Manazuru, Kanagawa Prefecture
May 19 Okinawa OWS in Okuma Beach 750m/1.5km/2.5km/


May 27 28th International Cocos Island crossing, Guam 3km/5km/10km Guam


June 3 Shizuoka OWS Rarara Sunbeach 1km/2.5km/5km

(It’s possible to do all 3 distances back to back)

Shizuoka Prefecture
June 10 4th Annual Chiba Futtsu OWS 750m/1.5km/3km Futtsu, Chiba Prefecture
June 17 1st Okinawa Cape Kiyan Itoman OWS 500m/1km/1.5km/3km Okinawa
June 24 5th Annual Yokosuka OWS 500m/1km/2km Yokosuka, Kanagawa prefecture
June 24 Nakaumi OWS 3km/5km Yonago, Tottori Prefecture
June 30 Rough Water swim in Oiso Terugasaki 800m/1.5km/3km Oiso, Kanagawa prefecture

July OWS

July 1 Oiso Long beach swim

(500m pool swim. Not a beach swim)


1km/3km/5km/10km Oiso, Kanagawa Prefecture





July 1 13th Annual Aichi OWS 500m/1km/1.5km/3km Aichi prefecture
July 7 24th annual Niijima OWS 1.5km/3km/4.5km Niijima island, Tokyo


July 7 Miyakejima OWS 2.5km/5km Miyakejima island Not yet open. Date is tentative.
July 7 Rough water swim in Kamakura 800m/1.5km/3km Kamakura, Kanagawa prefecture
July 7 5th Annual Katsuura swim festa OWS 1/5km/3km Mobara beach, Chiba prefecture
July 7 6th Annual World Heritage Yakushima OWS 1km/2.5km/5km Yakushima, Kyushu prefecture
July 8 4th Annual World Heritage Kumano Kodo OWS 500m/1km/1.5km/3km Mie prefecture
July 8 Hayama OWS 1.5km/3/4.5km   Entry:




July 14 10th Annual Manazuru OWS 500m/1.5km/3km Manazuru
July 15 4th Annual Amakusa Takarajima 500m/1km/1.5km/3km Kumamoto prefecture
July 15-16 Tateyama swim festival 1km/2km/3km/5km Tateyama, Chiba prefecture
July 22 3rd Annual Udon ken Sanuki OWS 500m/1km/1.5km/3km Kagawa prefecture
July 29 OWS Mie prefecture – Owase 500m/1km/3km/5km Mie prefecture

August 2018

Aug 5 2nd Kamaishi OWS, Nebama beach 500m/1km/3km/5km Kamaishi, Iwate prefecture
Aug 12 Miura Suika OWS 1.5km/3km/5km Miura Kaigan, Kanagawa prefecture
Aug 19 2nd Annual Tokyo Bay OWS 1.5km Tokyo
Aug 19 1st Yokohama Umi no Koen Aquathlon


750m swim + 4km run

1.5km swim + 8km run

1.5km swim (OWS only)

Yokohama, Kanagawa prefecture
Aug 19 6th Annual Osaka Sennan OWS 500m/1km/1.5km/3km Osaka
Aug 25 SwimRun Japan   Gunma prefecture Entries not open yet
Aug 26 3rd Annual Lake Inawashiro swim 3km Lake Inawashiro, Fukushima prefecture

Sep 2018

Sep 1 15th Annual Shonan OWS 10km marathon swim

Point to point swim from Zushi to Enoshima.

A very tough race with a 3.5hr time limit

Kanagawa prefecture.


Not open yet
Sep 2 Shonan 2.5km OWS 2.5km Zushi beach, Kanagawa prefecture Not open yet
Sep 2 1st Setouchi Awaji Island OWS 500m/1km/1.5km/3km Awaji Island, Hyogo prefecture
Sep 9 24th Annual Atami OWS Grand Prix 500m/1km/1.5km/3km Atami beach, Shizuoka prefecture
Sep 23 12th Annual Minami Boso OWS 500m/1km/1.5km/3km Chiba prefecture
Sep 30 2nd Annual Tsuruga Bay Osezaki OWS 500m/1km/1.5km/3km Shizuoka prefecture

October 2018

Oct 1 Setouchi OWS in Shibukawa 500m/1km/2km/5km Shibukawa, Okayama prefecture
Oct 10 3rd Annual World Heritage Okinawa “Sefa Utaki” OWS


(Azama SunSun beach)

500m/1km/1.5km/3km Okinawa
Oct 27 Ishigaki Island OWS 500m/1km/2.5km/5km


Ishigakijima, Okinawa
Oct 6 Tokyo Summerland Swim

(Pool swim)

1km/3km/5km/10km Tokyo
Oct 29 Susaki OWS 200m/1km/3km/5km Susaki, Kochi prefecture




Bonus international open water swim events in amazing locations: check out SwimJunkie OWS races in the Philippines.

2015 Open Water swimming calendar.

i prefecture for this race. It looks cool.

5 September: The annual Onjuku 3.8km swim. Entries not yet open but this swim is tradition and we get a good crowd to come along and do this race.

5 December: Palau. A Palau swim race is on my to-do list this year. 5km distance. Have already paid for the airfare, but have not yet registered for the race. Would like to do an Okinawa swim race at some point as well.

2014 Japan Open Water Swimming Race Calendar

June 1 – Guam Cocos Island Crossing 2.5 mile one-way crossing 5 mile two-way crossing (NB time limit of 2hr 45min) Entries are open here

June 15 – Minami Boso Aquathlon Short course: 500m swim + 5km run Long course; 1.5km + 10km Entries open here.

July 12 – Niijima Island Open Water Swim race Distance options: 1.5km/3km/4.5km — 2013 race calender

May 19 Aquathlon – First Annual South Atami beach Aquathlon, Nagaham beach (Shizuoka prefecture) Short course: 500m swim + 5km run Long course: 1.5km + 10km run

May 25 – Guam – International Cocos Island Crossing Distance: 2.5 mile/5 mile Entries open here

June 2 – 2nd Annual Minami Boso Aquathlon (Chiba prefecture), Iwai beach Short course: 500m swim + 5km run Long course: 1.5km swim + 10km run

June 15-16 – 3rd Annual 沖縄美ら Sun beach OWS race Okinawa 沖縄県豊見城市豊崎海浜公園 Distances: 400m/800m/1500m

June 23 – Fukui prefecture Takasu Fukui beach OWS Distance: 800m/2km Entries open here

June 23 – 4th Annual Izu Yumigahama OWS race Shizuoka prefecture (Izu) Yumigahama beach Distances: 1km/2km/400m×4Relay June 30 – First annual Chiba prefecture Inage beach OWS Distances: 1km/2km/1mileRelay

July 7 – Kanagawa prefecture Oiso beach OWS Distances: 1km/3km/5km/10km Entries open here

July 7 – 19th Annual Atami OWS Japan Grand Prix – Shizuoka prefecture, Atami beach Distance: 400m/800m/3200m/500m×4Relay July 14 – First Fukuoka prefecture Shikanoshima beach OWS race Distance: 400m/800m/1,500m/3,000m

July 21 – Shizuoka OWS Distances: 1km/2km Entries open here

July 21 – 8th Annual Aichi prefecture Ono beach (Rurigahama) OWS race Distance: 400m/1,000m/3,000m/400m×4Relay August 10 – Miura Suika (watermelon) OWS race Distances: 1.5km/3km Entries open here

August 18 – 7th Annual Biwa lake swim (Hyogo Prefecture) Distance: 400m/800m/3,000m/400m×4Relay

September 1 – 3rd Annual International Masters OWS Yumigahama (Shizuoka prefecture, Yumigahama beach (Izu) Distance: 400m/800m/3,000m/400m×4Relay

September 15 – 6th Annual Chiba prefecture Minami Boso beach OWS race Distance: 400/1km/3km/400m×4Relay

September 15 – Kanagawa prefecture Oiso Long beach OWS (National Open Water Swimming Qualifying race – Pro race. Time limits apply) Distances: 5km/10km Info here

September 23 – 2nd Annual Aichi prefecture Aquathlon race, Chidorigahama beach Short course: 500m swim + 5km run Long course: 1.5km swim + 10km run

October 13 – 4th Annual Izu Aquathlon, Yumigahama beach Short course: 500m swim + 4.5km swim Long courde: 1.5km swim + 7.5km swim

October 19 (Day 1) -3rd Annual Okinawa Kumejima Island OWS race Distance: 400m/800m/1,500m/1mile Relay

October 20 (Day 2) – 3rd Annual Okinawa Kumejima Island OWS race Distance: 5km/10km ——————

2012 Open Water Swimming Event Calendar (as translated by me).

Any questions, let me know via the Contact page. 2012 OWS race calendar (excluding races in Okinawa).

June 3 – 1st Minami Boso Aquathlon Iwai beach (Chiba beach). 500m swim + 5km run OR 1.5km + 10km run. Alternatively you can do just the 10km or just the 1.5km swim. Entries open. 9 – 2nd Annual Izu Matsuzaki Ocean swim (Shizuoka prefecture). 1.5km/3km. Entries open here. Official site here. 24 – 3rd Minami Izu Yumigahama OWS (Shizuoka prefecture). 1km/2km. Entries open. July

2 – Second annual Miura kaigan ocean swim 7 –

Niijima Island OWS – 1.5km/3km/4.5km (See Race Reports for an account of the 4.5km swim). 7-8 – Kamakura rough water series – 800m/1.5km/3km

8 – 18th Atami OWS Japan Grand prix – 400m/800m/3.2km. Entries open. Nice flat bay swim.

8 – Oiso Event, Long Beach (Shizuoka prefecture). 500m/1.5km/3km/10km. It’s held in a wave pool. Official site here. Entries open.

8 – 2nd annual Takeno OWS (Hyogo prefecture). 1km/2.5km. Entries open. 8 – Saikai 99 islands (Pearl Sea) in Nagasaki. 800m/1.5km (July 7 and 8 a big weekend for open water swims)

15 – Sakurajima (Kagoshima) OWS. 15 – Japan OWS 2012 Championships. Tateyama (Chiba prefecture). Hosted by the Japan Swimming Federation. More info released later. Check back into their website.

22 – Aichi prefecture OWS – 400m/800m/3.2km. Entries open.

22 – Miho OWS. 1km/2km. Entries open. I don’t recommend this one. Save your money and time.

11 – Miura Kaigan swim. 1.5km/3km. Entries open. Official website. Great beach. Shame about the water quality. Won’t be swimming at Miura ever again.

19 – Lake Biwa swim – (Shiga prefecture). 500m/1km/3.2km. Entries open. Official website.

25 – First Fukui swim. 400m/800m/2km. Entries open. Official site.

26 – First Fukuoka Shikanoshima swim. 400m/800m/1.6km/3.2km. Entries here.

26 – Shonan OWS race. (Kanagawa prefecture). 2.5km (10,000yen) or 10km (20,000yen). 2.5km starts at Shichirigahama beach and ends at 瀬東浜. Website here 10km swim starts at Zushi beach and ends at 瀬東浜. Time limit for 10km is 3.5 hours. September 1 – Kozushima aquathlon – 1.5km swim + 10km OR 750m swim + 5km run 9 – 2nd OWS Masters, Yumigama beach (Shizuoka prefecture) – 400m/800m/3km. Nice location. Entries open.

16 – Minami Boso (Chiba) beach swim – 400m/1km/3km. Entries open. Good solid classic beach swim. Recommend.

30 – Atami One-mile championship (Shizuoka prefecture) – 100m/400m/1.6km. Entries open.

October 2 – Minami Izu Aquathlon Yumigahama (Shizuoka prefecture). 500m swim + 4.5km run OR 1.5km swim + 7.5km OR 1.5km swim + 7.5km run. Entries open. The OWS season ends by October on Honshu (mainland Japan). However, if you’re still keen, Okinawa has 4 events during the month of October that you can partake in.

Other recommended websites: Roughwater Swim Series (5-6 events), by PowerSports. MSPO Tokyo Island series. Well organized and interesting locations. Events consist of triathlons, open water swimming and aquathlons.

2011 OWS race calendar.

May 28 (Saturday) – Aquathlon Shikinejima (Shikine Island) Option A – 1.5km swim + 10km run Option B – 750m swim + 5km run Cost: 8000yen per race. Location: Shikine Island. (A tiny island off Tokyo) Race info here (MSPO)

June 11 Izu Matsuzaki OWS JIOWSA Distance: 1.5km/3km Cost: 5000/7000yen Entry here.

June 12 (Sunday) 2nd Izu National Park Yumigahama OWS race Distances/cost: 400m (2000yen)/800m (5000yen)/1.6km (6000yen)/3.2km (8000yen) Relay: 1.6km (400m x 4ppl) (6000yen) (Late entry April 13-May 31 – cost extra 1000yen) Online entry here.

June 18-19 Okinawa Sun beach OWS Distances: 400m/800/1.6km/3.2km Entry here.

July 2 Miura Seaside Beach swim (Kanagawa prefecture) Distances: 1.5km/3km Online entry here.

July 3 (Sunday) 2nd Long Beach OWS (Kanagawa Prefecture) Distances: 500m/1.5km/3km/10km. Technically, this is not a beach swim….it’s a very long special pool swim…I think (Time limits apply for each distance) Deadline: May 3 Extra admission/entry for Long Beach -3000yen July 9 Kamakura rough water swim Distances; 3km (entries closed)/1.5km / 800m Online entry here. Race info here.

July 9 Nijima Island OWS Distances: 1.5km/3km/4.5km Cost: 5000yen Info here. Entry form can be downloaded from the site above. Send application form by post. Payment can be made by furikomi.

July 10 17th Annual Atami Sun beach OWS (Shizuoka) Distance: 400m/800m/3.2km 3.2km = 8000yen Entry here.

July 16 Open water swimming in Azigaura race (Ibaragi prefecture) (First time this event is being held in support of the Japan Tohoku disatser relief effort campaign) Distance: 2km (6000yen)/4km (8000yen) Entry here. Race info/website here.

July 24 (Aichi prefecture) 400m/1km/3km Online entry here. Race info here.

July 24 NAC Big Swim in Lake Toya 800m/1.5km *Note: freshwater lake swim. Water temps on the cooler side. Fun day. Great BBQ spread afterwards, t-shirt, and great lucky dip prizes to be won.

July 31 Miho beach (Shizuoka beach) 400m/1km/2km (I, personally, do not recommend this event)

July 31 12th Pumpkin Competition Marathon OWS (Kanagawa prefecture, Miura area) Distance/cost: 1km (3000yen)/5km (7000yen) Capacity reached. Join the waiting list here in case someone cancels. This race seems popular. It filled up months in advance. Official website here.

August 4 Fukui prefecture, Takasu 2nd OWS 400m/1km/2km

August 7 Miyagi prefecture (Okumatsushima) 5th OWS event – CANCELLED 400m/800m/1.6km/3.2km

August 21 Lake Biwa swim (Shiga prefecture) NB: Lake swim. JIOWSA event. 400m/1km/3km Entry here.

Sep 3 OWS in Okinawa.

Sep 4 Minami Boso OWS. JIOWSA event. 400m/1km/3km Deadline: July 22 8000yen Online entry here.

Sep 11 1st International Masters OWS Yumigahama. JIOWSA event 800m/3km (FINA Masters ) Deadline: July 22 8000yen

Oct 2 Yumigahama Aquathlon. JOIWSA event Option A: 500m swim + 3km run Option B: 1.5km + 4.5km run. Online entry here. (Fun. And a great beginner entry into aquathlons)

I also highly recommend the Tokyo Island Series – a series of events ranging from open water swims to aquathlons and triathlons on the Seven Islands of Tokyo – interesting and beautiful locales. Not an exhaustive list (but pretty close to it).

I have left out most of the races which are in Okinawa, another good half dozen or so because I don’t plan on competing in them, I can’t be bothered translating them. If you need info, let me know. Tip: Get your entries in way in advance. Most close a month or two before the event day. On day registrations are available at a higher entry cost. Most races also have a participant limit of about 100-150 people per distance event. If numbers fill up quickly, registrations will close earlier. Sportsentry website sometimes has a waiting list (cancellations etc). Otherwise try your luck by turning up on the day)