# Classification of rivers in Japan

Rivers in Japan are classified according to criteria set by the River Act (河川法, Kasen Hō), which was introduced in 1967. Rivers are classified by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

## River Act
### Pre-1967 river administration

At the beginning of the Meiji era, river construction mainly consisted of low water construction such as securing water for boat transportation and irrigation, but after the middle of the Meiji era, boat transportation declined with the spread of railways, and on the other hand, development of river coasts exacerbated damage from floods. As the number of floods increased, a shift was made to high water construction to prevent flooding by building levees.
The old system was enacted in 1891 following the proclamation of the Meiji Constitution. As Japan's first modern public property management system, a systematic legal system for river management was established. However, due to the background of its enactment, the old River Law had strong overtones of control by state power, and, reflecting the social situation at the time, placed more emphasis on flood control than water utilization.

### New River Act

Over the following 70 years, due to post-war social and economic development, the use of river water for hydroelectric power generation and industrial water increased rapidly and because of inconsistencies that had arisen in the system implemented by the old River Act, the new River Act was enacted in 1962, with the following changes:
* All rivers and river systems are classified into four classes
* Entities in charge of rivers are required to formulate a plan for integrated water management
* Establishment of regulations related to water use
* Establishment of regulations to prevent disasters caused by dams

### 1997 amendment

The River Act was amended in 1997, changing its text to have a greater emphasis on conservation of natural environments, and the consultation and participation of local residents in forming water management plans.

### Impact

The 1967 River Act simplified the management of waterways in Japan by merging previously separate systems into one unified water management system. Before this, the river management system in Japan was seen as heavy-handed and overly bureaucratic. Especially post-1997 amendment, there is now greater community involvement when formulating plans regarding rivers and water management.

## Class A rivers

Class A river system (一級水系, Ikkyū suikei) is a designation applied to rivers systems deemed to be important to the economy of the nation as a whole, as well as those deemed important to the conservation of nature within Japan. There are currently 109 river systems with this designation. If a river system is designated Class A, all the constituent rivers are also designated as such. Therefore, Class B rivers cannot coexist with Class A rivers in the same river system. This designation is also called First Class.
Class A river (一級河川, Ikkyū kasen) is a designation which applies to important individual rivers. There are 13,994 rivers with this designation.
Generally speaking, areas surrounding Class A rivers will suffer greater damage in the event of a flood.

### List of Class A river systems

The number of dams only includes existing and unestablished dams that meet the criteria (15 metres (49 ft) or more in bank height) of the River Law. The management entity is irrelevant. The number in parentheses is the number of dams on the main river, excluding tributaries. The number of dams does not always exceed the number of hydroelectric plants because plants with intake weirs less than 15 metres (49 ft) high are not considered dams. The acronym BOD refers to biochemical oxygen demand.
Note: Okinawa has no Class A rivers.

#### Hokkaidō Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Teshio | 天塩川 | 256 | 5,590 | Hokkaidō | 94,000 | 160 | 134.52 | 0.7 | 14 (2) | 3 |
| Shokotsu | 渚滑川 | 84 | 1,240 | Hokkaidō | 28,000 | 25 | 29.33 | 1.0 | 0 | 2 |
| Yūbetsu | 湧別川 | 87 | 1,480 | Hokkaidō | 36,000 | 17 | 32.45 | 1.7 | 1 (0) | 3 |
| Tokoro | 常呂川 | 120 | 1,930 | Hokkaidō | 142,000 | 57 | 22.64 | 2.6 | 2 (1) | 0 |
| Abashiri | 網走川 | 115 | 1,380 | Hokkaidō | 94,000 | 25 | 14.02 | 2.5 | 1 (0) | 2 |
| Rumoi | 留萌川 | 44 | 270 | Hokkaidō | 28,000 | 13 | 11.84 | 1.5 | 3 (0) | 0 |
| Ishikari | 石狩川 | 268 | 14,330 | Hokkaidō | 2,500,000 | 464 | 133.18 | 1.1 | 83 (1) | 34 |
| Shiribetsu | 尻別川 | 126 | 1,640 | Hokkaidō | 38,000 | 40 | 68.41 | 0.4 | 3 (0) | 7 |
| Shiribeshi-Toshibetsu | 後志利別川 | 80 | 720 | Hokkaidō | 16,000 | 29 | 23.69 | 0.5 | 2 (1) | 8 |
| Mu | 鵡川 | 135 | 1,270 | Hokkaidō | 13,000 | 20 | 38.54 | 0.6 | 2 (0) | 1 |
| Saru | 沙流川 | 104 | 1,350 | Hokkaidō | 13,000 | 28 | 48.24 | 0.6 | 4 (2) | 4 |
| Kushiro | 釧路川 | 154 | 2,510 | Hokkaidō | 177,000 | 38 | 26.32 | 1.7 | 0 | 0 |
| Tokachi | 十勝川 | 156 | 9,010 | Hokkaidō | 340,000 | 209 | 85.36 | 1.7 | 14 (3) | 16 |

#### Tōhoku Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Iwaki | 岩木川 | 102 | 2,540 | Aomori | 482,400 | 97 | 76.07 | 1.6 | 21 (2) | 5 |
| Takase | 高瀬川 | 64 | 867 | Aomori | 80,372 | 23 | 50.10 | 0.9 | 3 (1) | 0 |
| Mabechi | 馬淵川 | 142 | 2,050 | Iwate, Aomori | 188,000 | 30 | 47.62 | 1.1 | 6 (0) | 5 |
| Kitakami | 北上川 | 249 | 10,150 | Iwate, Miyagi | 1,389,000 | 302 | 318.42 | 1.1 | 53 (1) | 33 |
| Naruse | 鳴瀬川 | 89 | 1,130 | Miyagi | 190,000 | 61 | 26.49 | 1.3 | 13 (1) | 3 |
| Natori | 名取川 | 55 | 939 | Miyagi | 1,125,589 | 30 | 17.32 | 1.1 | 9 (0) | 7 |
| Abukuma | 阿武隈川 | 239 | 5,400 | Miyagi, Fukushima | 1,380,000 | 197 | 52.22 | 1.9 | 19 (2) | 25 |
| Yoneshiro | 米代川 | 136 | 4,100 | Akita, Iwate | 280,000 | 89 | 100.91 | 1.3 | 21 (0) | 22 |
| Omono | 雄物川 | 133 | 4,710 | Akita | 346,481 | 168 | 259.02 | 1.4 | 34 (0) | 17 |
| Koyoshi | 子吉川 | 61 | 1,190 | Akita | 80,000 | 44 | 60.60 | 1.1 | 12 (1) | 7 |
| Mogami | 最上川 | 229 | 7,040 | Yamagata | 999,300 | 429 | 369.26 | 1.0 | 41 (1) | 26 |
| Aka | 赤川 | 70 | 857 | Yamagata | 109,294 | 44 | 65.68 | 1.0 | 5 (1) | 10 |

#### Kantō Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Kuji | 久慈川 | 124 | 1,490 | Fukushima, Ibaraki | 201,981 | 53 | 23.58 | 0.8 | 1 (0) | 7 |
| Naka | 那珂川 | 150 | 3,270 | Tochigi, Ibaraki | 912,217 | 197 | 74.43 | 0.9 | 22 (2) | 12 |
| Tone | 利根川 | 322 | 16,840 | Gunma, Nagano, Tochigi, Saitama, Tokyo, Chiba, Ibaraki | 12,140,000 | 819 | 237.10 | 2.5 | 70 (4) | 98 |
| Ara | 荒川 | 173 | 2,940 | Saitama, Tokyo | 9,300,000 | 127 | 27.77 | 4.4 | 13 (2) | 11 |
| Tama | 多摩川 | 138 | 1,240 | Yamanashi, Tokyo, Kanagawa | 4,250,000 | 52 | 40.28 | 1.7 | 2 (2) | 5 |
| Tsurumi | 鶴見川 | 43 | 235 | Tokyo, Kanagawa | 1,840,000 | 11 | 7.83 | 8.0 | 0 | 0 |
| Sagami | 相模川 | 113 | 1,680 | Yamanashi, Kanagawa | 1,200,000 | 104 | － | 2.0 | 10 (3) | 20 |
| Fuji | 富士川 | 128 | 3,990 | Nagano, Yamanashi, Shizuoka | 1,600,000 | 555 | 58.91 | 2.3 | 19 (0) | 71 |

#### Hokuriku Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Ara | 荒川 | 73 | 1,150 | Yamagata, Niigata | 40,000 | 61 | 115.00 | 0.6 | 5 (3) | 6 |
| Agano | 阿賀野川 | 210 | 7,710 | Fukushima, Gunma, Niigata | 590,000 | 243 | 401.55 | 0.6 | 62 (8) | 60 |
| Shinano | 信濃川 | 367 | 11,900 | Nagano, Gunma, Niigata | 2,950,000 | 880 | 503.15 | 1.0 | 90 (1) | 122 |
| Seki | 関川 | 64 | 1,140 | Nagano, Niigata | 210,000 | 78 | 50.32 | 1.5 | 5 (1) | 16 |
| Hime | 姫川 | 60 | 722 | Nagano, Niigata | 20,000 | 47 | 44.07 | 0.5 | 0 | 19 |
| Kurobe | 黒部川 | 85 | 682 | Toyama | 71,000 | 25 | 37.00 | 0.8 | 6 (5) | 18 |
| Jōganji | 常願寺川 | 56 | 368 | Toyama | 30,000 | 49 | 16.23 | 0.6 | 8 (1) | 27 |
| Jinzū | 神通川 | 120 | 2,720 | Gifu, Toyama | 380,000 | 105 | 183.65 | 1.4 | 25 (7) | 60 |
| Shō | 庄川 | 115 | 1,180 | Gifu, Toyama | 28,032 | 48 | 47.72 | 1.0 | 18 (9) | 27 |
| Oyabe | 小矢部川 | 68 | 667 | Ishikawa, Toyama | 300,000 | 64 | 27.99 | 1.5 | 14 (2) | 5 |
| Tedori | 手取川 | 72 | 809 | Ishikawa | 40,000 | 35 | 77.21 | 0.5 | 7 (2) | 24 |
| Kakehashi | 梯川 | 42 | 271 | Ishikawa | 110,000 | 13 | 18.02 | 1.0 | 1 (1) | 0 |

#### Chūbu Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Kano | 狩野川 | 46 | 852 | Shizuoka | 640,000 | 76 | 21.40 | 1.5 | 0 | 7 |
| Abe | 安倍川 | 51 | 567 | Shizuoka | 170,000 | 36 | 41.44 | 0.8 | 0 | 2 |
| Ōi | 大井川 | 168 | 1,280 | Shizuoka | 90,000 | 39 | 76.40 | 0.5 | 14 (7) | 15 |
| Kiku | 菊川 | 28 | 158 | Shizuoka | 70,000 | 25 | 2.21 | 1.8 | 2 (0) | 0 |
| Tenryū | 天竜川 | 213 | 5,090 | Nagano, Aichi, Shizuoka | 720,000 | 332 | 239.67 | 0.5 | 17 (5) | 51 |
| Toyo | 豊川 | 77 | 724 | Aichi | 210,000 | 27 | 28.23 | 0.6 | 9 (1) | 3 |
| Yahagi | 矢作川 or 矢矧川 | 118 | 1,830 | Nagano, Gifu, Aichi | 690,000 | 94 | 43.99 | 1.0 | 25 (3) | 25 |
| Shōnai | 庄内川 | 96 | 1,010 | Gifu, Aichi | 2,500,000 | 76 | 26.21 | 4.7 | 18 (0) | 2 |
| Kiso | 木曽川 | 229 | 9,100 | Nagano, Gifu, Shiga, Aichi, Mie | 1,700,000 | 391 | 291.05 | 0.7 | 64 (9) | 77 |
| Suzuka | 鈴鹿川 | 38 | 323 | Mie | 110,000 | 46 | 11.23 | 1.4 | 0 | 0 |
| Kumozu | 雲出川 | 55 | 550 | Mie | 90,000 | 40 | 14.36 | 1.6 | 6 (0) | 1 |
| Kushida | 櫛田川 | 85 | 461 | Mie | 40,000 | 68 | 20.55 | 0.7 | 4 (0) | 5 |
| Miya | 宮川 | 91 | 920 | Mie | 140,000 | 55 | 45.70 | 0.5 | 5 (2) | 6 |

#### Kinki Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Kuzuryū | 九頭竜川 | 116 | 2,930 | Gifu, Fukui | 666,225 | 147 | 108.26 | 0.8 | 20 (3) | 25 |
| Kita | 北川 | 30 | 211 | Shiga, Fukui | 21,389 | 12 | 11.68 | 0.6 | 1 (0) | 1 |
| Yura | 由良川 | 146 | 1,880 | Hyōgo, Kyōto | 300,000 | 138 | 52.09 | 0.8 | 22 (3) | 6 |
| Yodo | 淀川 | 75 | 8,240 | Shiga, Kyōto, Ōsaka, Mie, Nara, Hyōgo | 11,650,000 | 965 | 267.51 | 1.9 | 66 (1) | 34 |
| Yamato | 大和川 | 68 | 1,070 | Nara, Ōsaka | 2,150,000 | 178 | 23.94 | 3.3 | 11 (1) | 0 |
| Maruyama | 円山川 | 68 | 1,300 | Hyōgo | 150,557 | 97 | 37.40 | 0.9 | 7 (0) | 5 |
| Kako | 加古川 | 96 | 1,730 | Hyōgo | 640,000 | 130 | 45.89 | 2.6 | 19 (0) | 0 |
| Ibo | 揖保川 | 70 | 810 | Hyōgo | 200,000 | 47 | 29.04 | 0.8 | 4 (0) | 6 |
| Kino | 紀の川 | 136 | 1,750 | Nara, Wakayama | 689,000 | 181 | 58.77 | 2.1 | 9 (2) | 6 |
| Kumano | 熊野川 | 183 | 2,360 | Nara, Mie, Wakayama | 84,000 | 103 | 163.54 | 1.3 | 11 (5) | 30 |

#### Chūgoku Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Sendai | 千代川 | 52 | 1,190 | Tottori | 200,000 | 87 | 61.68 | 0.8 | 6 (0) | 17 |
| Tenjin | 天神川 | 32 | 490 | Tottori | 65,500 | 32 | 24.03 | 1.2 | 8 (0) | 8 |
| Hino | 日野川 | 77 | 870 | Tottori | 60,800 | 56 | 33.55 | 1.1 | 12 (0) | 14 |
| Hii | 斐伊川 | 153 | 2,070 | Shimane, Tottori | 435,000 | 227 | 40.26 | 1.4 | 24 (2) | 13 |
| Gōno | 江の川 | 194 | 3,900 | Hiroshima, Shimane | 202,000 | 293 | 75.17 | 0.8 | 20 (2) | 24 |
| Takatsu | 高津川 | 81 | 1,090 | Shimane | 38,600 | 92 | 51.88 | 0.7 | 4 (0) | 5 |
| Yoshii | 吉井川 | 133 | 2,110 | Okayama | 294,000 | 215 | 61.16 | 2.0 | 30 (1) | 18 |
| Asahi | 旭川 | 142 | 1,810 | Okayama | 335,000 | 147 | 57.01 | 1.8 | 25 (3) | 9 |
| Takahashi | 高梁川 | 111 | 2,670 | Okayama, Hiroshima | 273,000 | 121 | 61.81 | 2.5 | 29 (1) | 19 |
| Ashida | 芦田川 | 86 | 860 | Okayama, Hiroshima | 269,000 | 82 | 12.73 | 4.0 | 18 (2) | 3 |
| Ōta | 太田川 | 103 | 1,710 | Hiroshima | 980,000 | 73 | 78.81 | 0.9 | 11 (2) | 24 |
| Oze | 小瀬川 | 59 | 340 | Hiroshima, Yamaguchi | 26,500 | 23 | 12.05 | 2.6 | 4 (2) | 6 |
| Saba | 佐波川 | 56 | 460 | Yamaguchi | 31,100 | 32 | 18.69 | 0.7 | 4 (1) | 1 |

#### Shikoku Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Yoshino | 吉野川 | 194 | 3,750 | Kōchi, Ehime, Tokushima, Kagawa | 641,000 | 356 | 107.67 | 0.8 | 23 (4) | 32 |
| Naka | 那賀川 | 125 | 874 | Tokushima | 59,000 | 75 | 62.88 | 0.7 | 4 (3) | 5 |
| Doki | 土器川 | 33 | 140 | Kagawa | 35,000 | 11 | 1.83 | 3.9 | 2 (0) | 0 |
| Shigenobu | 重信川 | 36 | 445 | Ehime | 233,000 | 75 | 2.24 | 5.0 | 8 (0) | 1 |
| Hiji | 肱川 | 103 | 1,210 | Ehime | 112,000 | 475 | 37.61 | 1.0 | 8 (2) | 4 |
| Monobe | 物部川 | 71 | 508 | Kōchi | 40,000 | 35 | 30.78 | 0.7 | 4 (3) | 6 |
| Niyodo | 仁淀川 | 124 | 1,560 | Ehime, Kōchi | 105,000 | 166 | 100.07 | 0.7 | 5 (3) | 18 |
| Shimanto | 四万十川 | 196 | 2,270 | Ehime, Kōchi | 100,000 | 319 | 121.02 | 0.6 | 5 (0) | 6 |

#### Kyūshū Development Bureau

| Name | Japanese | Main stream length (km) | Basin area (km$^2$) | Basin management | Basin area population | Tributaries | Average annual flow rate (m$^3$/s) | BOD (ppm) | Dams | Hydroelectric plants |
| Onga | 遠賀川 | 61 | 1,026 | Fukuoka | 666,406 | 74 | 31.47 | 2.6 | 23 (0) | 1 |
| Yamakuni | 山国川 | 56 | 540 | Ōita, Fukuoka | 36,801 | 39 | 20.81 | 0.9 | 1 (0) | 1 |
| Chikugo | 筑後川 | 143 | 2,863 | Kumamoto, Ōita, Fukuoka, Saga | 1,090,777 | 235 | 95.09 | 1.6 | 29 (2) | 22 |
| Yabe | 矢部川 | 61 | 647 | Fukuoka | 182,889 | 23 | 21.54 | 1.1 | 17 (2) | 4 |
| Matsuura River | 松浦川 | 47 | 446 | Fukuoka, Saga | 97,818 | 80 | 12.46 | 2.4 | 22 (0) | 3 |
| Rokkaku | 六角川 | 47 | 341 | Saga | 122,827 | 79 | 4.36 | 2.1 | 9 (1) | 0 |
| Kase | 嘉瀬川 | 57 | 368 | Saga | 133,412 | 51 | 14.10 | 1.0 | 3 (2) | 8 |
| Honmyō | 本明川 | 21 | 87 | Nagasaki | 54,583 | 18 | 2.11 | 1.8 | 2 (1) | 0 |
| Kikuchi | 菊池川 | 71 | 996 | Kumamoto | 208,694 | 68 | 39.56 | 1.1 | 1 (0) | 4 |
| Shira | 白川 | 74 | 480 | Kumamoto | 131,375 | 16 | 25.39 | 2.5 | 3 (1) | 4 |
| Midori | 緑川 | 76 | 1,100 | Kumamoto | 517,189 | 59 | 36.17 | 2.4 | 4 (2) | 11 |
| Kuma | 球磨川 | 115 | 1,880 | Kumamoto | 137,375 | 82 | 119.92 | 1.4 | 11 (4) | 20 |
| Ōita | 大分川 | 55 | 650 | Ōita | 252,808 | 48 | 22.33 | 1.4 | 7 (1) | 14 |
| Ōno | 大野川 | 107 | 1,465 | Kumamoto, Miyazaki, Ōita | 206,818 | 138 | 61.36 | 0.6 | 14 (0) | 10 |
| Banjō | 番匠川 | 38 | 464 | Kumamoto, Miyazaki, Ōita | 56,527 | 52 | 12.17 | 1.1 | 5 (0) | 0 |
| Gokase | 五ヶ瀬川 | 106 | 1,820 | Miyazaki | 127,638 | 102 | 60.94 | 1.1 | 8 (2) | 22 |
| Omaru | 小丸川 | 75 | 474 | Miyazaki | 32,616 | 16 | 32.76 | 0.5 | 8 (4) | 5 |
| Ōyodo | 大淀川 | 107 | 2,230 | Kagoshima, Miyazaki | 601,321 | 134 | 107.61 | 1.3 | 16 (2) | 12 |
| Sendai | 川内川 | 137 | 1,600 | Kumamoto, Miyazaki, Kagoshima | 195,944 | 129 | 91.09 | 0.7 | 4 (3) | 5 |
| Kimotsuki | 肝属川 | 34 | 485 | Kagoshima | 115,578 | 36 | 31.69 | 4.5 | 2 (0) | 3 |

## Class B rivers

Smaller or less important rivers are designated as Class B river systems (二級水系, Nikyū Suikei). They are nominated and managed by the local governments at the prefecture level, but reported to and concurred with by the central government. There are 7,090 rivers with this designation. Because all of their river systems are designated Class A, there are no Class B rivers in Saitama and Shiga prefectures.
This designation is also called Second Class.

## Mutatis mutandis rivers

14,314 rivers in Japan are designated as mutatis mutandis rivers (準用河川, Junyō kasen), meaning that they are not assigned Class A or B designation, and are under the control of the mayor of the encompassing municipality. An example of this is the Kuno River, managed by the mayor of Odawara.

## Ordinary rivers

Rivers that are not designated Class A, Class B, or mutatis mutandis, are called ordinary rivers (普通河川, Futsū kasen), and the 1967 River Act does not apply to them. These do not include public sewers or agricultural canals. Management of these rivers is carried out by the local municipality.