Cleanest lakes in Japan
Cleanest lakes in Japan: 188 named lakes have an official total-phosphorus reading. The 20 below carry the lowest nutrient load — a measurement, not a LakeQuality A–F grade.
Lake map
Lowest phosphorus readings in Japan
Phosphorus is the nutrient that feeds algae growth, so the lakes at the top of this table are the least loaded ones the Japan monitoring programme has measured. The median measured lake in Japan reads 13 µg/L.
| Lake | Place | Total phosphorus | Chlorophyll-a | Secchi | Year |
|---|---|---|---|---|---|
| 倶多楽湖 | Hokkaido | 3.0 µg/L | — | 17 m | 2024 |
| 境川ダム貯水池 | Toyama | 3.0 µg/L | — | 5.1 m | 2024 |
| 境川ダム貯水池 | Gifu | 3.0 µg/L | — | 5.1 m | 2024 |
| 支笏湖 | Hokkaido | 3.0 µg/L | — | 18 m | 2025 |
| 本栖湖 | Yamanashi | 3.0 µg/L | — | 14 m | 2025 |
| 洞爺湖 | Hokkaido | 3.0 µg/L | — | 13 m | 2024 |
| 田沢湖 | Akita | 3.0 µg/L | — | 10 m | 2024 |
| 十和田湖 | Aomori | 4.0 µg/L | — | 10 m | 2024 |
| 十和田湖 | Akita | 4.0 µg/L | — | 11 m | 2024 |
| 大橋ダム貯水池 | Kochi | 4.0 µg/L | — | — | 2024 |
| 奈良俣ダム貯水池 | Gunma | 4.0 µg/L | — | 5.5 m | 2024 |
| 有峰ダム貯水池 | Toyama | 4.0 µg/L | — | 3.3 m | 2024 |
| 池田湖 | Kagoshima | 4.0 µg/L | — | 8.0 m | 2025 |
| 沼沢湖 | Fukushima | 4.0 µg/L | — | 6.8 m | 2024 |
| 深山ダム貯水池 | Tochigi | 4.0 µg/L | — | 7.3 m | 2024 |
| 芦ノ湖 | Kanagawa | 4.0 µg/L | — | 7.8 m | 2025 |
| 青木湖 | Nagano | 4.0 µg/L | — | — | 2024 |
| 徳山ダム貯水池 | Gifu | 4.5 µg/L | — | — | 2024 |
| 中禅寺湖 | Tochigi | 5.0 µg/L | — | 7.8 m | 2024 |
| 奥只見貯水池 | Niigata | 5.0 µg/L | — | 6.0 m | 2024 |
Showing 20 of 188 named lakes. Open a county or place page for the rest.
Frequently asked questions
- Which lakes in Japan are the cleanest?
- 188 named lakes in Japan have an official total-phosphorus reading. This page ranks the 20 lowest. Phosphorus is the nutrient that feeds algae growth, so a low reading means a lightly loaded lake — it is not a swim-safety class and not a LakeQuality A–F grade.
- Why rank lakes by phosphorus?
- Phosphorus is usually what limits how much algae a lake can grow, so it is the earliest signal that a lake is under nutrient pressure. It is also the measurement these agencies publish most consistently, which makes it the fairest way to compare lakes across a country.
- Is a low-phosphorus lake safe to swim in?
- Not necessarily. A lightly loaded lake can still carry bacteria, a seasonal algal bloom, or contaminants that a nutrient reading does not cover. Check the local authority notice for the day you plan to go.
- What is a typical phosphorus level in Japan?
- The median measured lake in Japan reads 13 µg/L of total phosphorus. Lakes below roughly 10 µg/L are considered nutrient-poor and usually run clear; above about 30 µg/L a lake is generally nutrient-rich and more likely to green up in summer.
Cleanest lakes in other countries
Named lakes and official measurements
Directory of official lake water quality
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