Vegetarian's Japan Guide

A Guide to Shima Potholes, Momotarō Falls, and Shima Lake

If you are after a hot spring town in Gunma Prefecture where you can discover amazing natural scenery, Shima Onsen should top the list. The town is proud of what they call Shima Blue, a mysterious cobalt blue color that can be seen in most parts of Shima River on a sunny day. In particular, the below three spots can be easily accessed as they are located right next to the town’s main road!

Shima Potholes (四万の甌穴群)

Ⓒ ググっとぐんま観光宣伝推進協議会

Around 3km from Shima Onsen‘s town center, you will encounter eight potholes in Shima River. The potholes filled with river water are of a beautiful turquoise blue color that will enchant visitors. Surprisingly, this spot is easy to get to as it is located right next to the main road!

These potholes are formed naturally over a long period of time by stones or sand flowing in a circular direction due to the swirling flow of the river. It is just hard to imagine how many years it would take for the potholes to form, especially since the biggest one has a caliber of 3 meters and a depth of 4 meters!

If you look carefully, you might be able to find a small stone in the process of creating a new pothole with the help of the water flow! You should also be able to see small fish swimming in the river too!

When the Shima River isn’t flooded during the summer, you can head down to the riverbank to cool down. But if the siren goes off, retreat from the river bed as soon as possible, as more water from Shimagawa Dam is coming!

Note that the stairs down to Shima Potholes are frozen during the winter, so any access down to the river will be blocked for your safety. You can still, however, adore its beauty from the side of the road.

Ⓒ ググっとぐんま観光宣伝推進協議会

☛ The surface at the riverbank isn’t flat and can be slippery. Please walk carefully and choose your footwear wisely.
☛ Even if the day’s weather is fine, if it has rained the day before, there is a high chance that the river will be muddy.

The Best Time to Visit Shima Potholes

  • The river’s blue color is the most beautiful in April and May.
  • Autumn foliage season from late October to early November is another good time to visit Shima Potholes.

☛ Even if you come via public transportation, check out the parking lot. There might be stalls selling fresh vegetables and locally processed food! There is a toilet in the car park too.
☛ There are cherry blossom trees around Kiseki Forest Cafe (森のカフェKISEKI) at the car park.

How to Get to Shima Potholes

  • Shima Potholes is located in front of the bus stop, Shima Ōketsu-mae (四万甌穴前).

Momotarō Falls (桃太郎の滝)

Ⓒ 一般社団法人 四万温泉協会

While Momotarō Falls itself isn’t a magnificent waterfall, the surrounding scenery and the waterfall being a 2-minute walk down the river from the Shima Ōhashi Bridge would still be a spot worth your time. The scene of the small waterfall pouring into the tiffany blue river is just amazing to see!

Like Shima Potholes, Momotarō Falls is just by the side of the road. It is in front of you as soon as you get down the stairs. Just note that the spot isn’t related to the famous Japanese folk tale, Momotarō. While it can be hard to tell, the waterfall was named Momotarō because the water flow is divided into two parts and looks like a peach.

If you stay at Kashiwaya Ryokan, the stunning scenery is just a 5-minute walk away, perfect for a short stroll after checking in or for a morning walk!

How to Get to Momotarō Falls

  • Momotarō is a 5-minute walk from the bus stop, Shima Seiryu no Yu Iriguchi (清流の湯入口).
  • You can also trek from Shima Potholes, which will take around 15 minutes.
  • Although there is no designated parking lot for Momotarō Falls, there is a small parking space around 100 meters north of the waterfall.

四万湖 (Shima Lake)

Shima Lake is the dam lake of Nakanojō Dam (中之条ダム). Like Lake Okushima, the mysterious color of the lake water draws the hearts of those who see it.

The lake color also changes throughout the day depending on the light and time of day, making it a spot that you may want to return to multiple times when you visit Shima Onsen. You might also be able to snap a photo of Shima Lake with canoes floating!


If you are interested in participating in a canoe tour, contact Lakewalk by filling out the online form HERE. Although they only have a Japanese website, they have held tours for English speakers. You can translate the webpage using Google Chrome’s translation function at the right of the address bar.

For SUP tours, contact either of the below SUP tour operators:

☛ The scenery of Shima Lake is better from the bridge than from the dam. It is where you can see the most amazing cobalt blue color. You can walk to the bridge from Nakanojō Dam.
☛ There are a couple of cherry blossom trees close to the dam, although the area won’t have much greenery when the flower blooms.
☛ The spring green color is best in late May.

How to Get to Shima Lake

  • Momotarō is a 5-minute walk from the bus stop, Shimako (四万湖).

Kashiwaya Ryokan (柏屋旅館)

If you are after accommodation close to the above three spots, consider Kashiwaya Ryokan, which has perfected the classic formula of the wonderful Japanese ryokans!

The food, service, and onsen are all of superior high quality. What makes them truly exceptional is how accommodating and flexible the ryokan is. The staff there are respectful and welcoming, making you feel right at home!

For more information, refer to our article on Kashiwaya Ryokan!

Ⓒ 柏屋

Lake Okushima (奥四万湖)

Ⓒ 一般社団法人 四万温泉協会

Aside from the above three spots, there is one more place where you can adore the Shima Blue color at Shima Onsen. Lake Okushima, at the far back of the onsen town, is a great place to enjoy nature and watersports activities. The lake’s blue color is also deeper, giving you a different impression of the blue produced by nature.

For more information, refer to our article on Shimagawa Dam and Lake Okushima!

Discover Other Attractions at Shima Onsen

Whilst nature is definitely the selling point of Shima Onsen, the hot spring town has a couple of historical and cultural spots you might be interested in visiting. Furthermore, a ryokan is rumored to be the stage of the Ghibli movie ‘Spirited Away’!

So refer to our Shima Onsen article for where you can stop by during your time at the onsen town, including a couple of delicious places to try out!

Click the photo for more travel ideas at Shima Onsen!