Lake Akaya (赤谷湖, akayako) is one of the 100 best dam lakes in Japan located in north Gunma. This dam is drinking water for Tokyo. There is hot spring spots around the lake, so Akayako is Onsen spot, Sarugakyo Onsen(猿ケ京温泉), in north Gunma. In spring, you can enjoy Sakura, and in the fall there is beautiful autumn tint. All the mountain you can see from the lake will be changed its color to red and yellow in fall.
Tourist Info.
There is parking and restroom in the lake. You can enjoy hot spring spa around the lake.
Access
0. at Maebashi Station
1. use JR Ryoge line to Takasaki (15 min.)
2. use JS Joetsu Shinkansen to Jomokougen (17 min.)
3. use bus to Akayako
30 min
New Wave Samurai Movie. 
映画好き集まれ！ 
Around Lake Akaya, there is Sarugakyo Onsen where is great Onsen, hot spring spot. This Onsen was already travel spot in Edo Period. Because of construction of dam, the original village is under the water. However, the hot spring is still located above the water, so they moved the village and rename to Sarugakyo. Now, there are many hotels where you can enjoy great hot spring spa.