Gunma, Japan
County page for 12 named lakes in Japan. Official surface phosphorus, chlorophyll-a, and Secchi — not a swim-safety class and not a LakeQuality letter.
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Named lakes
| Lake | Place | Total phosphorus | Chlorophyll-a | Secchi | Year |
|---|---|---|---|---|---|
| 下久保ダム貯水池 | Gunma | 14 µg/L | — | 3.0 m | 2025 |
| 奈良俣ダム貯水池 | Gunma | 4.0 µg/L | — | 5.5 m | 2024 |
| 尾瀬沼 | Gunma | 6.0 µg/L | — | 3.7 m | 2024 |
| 桐生川ダム貯水池 | Gunma | 15 µg/L | — | 2.8 m | 2025 |
| 榛名湖 | Gunma | 9.0 µg/L | — | 5.2 m | 2024 |
| 相俣ダム貯水池 | Gunma | 7.0 µg/L | — | 3.0 m | 2025 |
| 矢木沢ダム貯水池 | Gunma | 6.0 µg/L | — | 5.5 m | 2024 |
| 草木ダム貯水池 | Gunma | 10 µg/L | — | 4.0 m | 2025 |
| 薗原ダム貯水池 | Gunma | 20 µg/L | — | 2.1 m | 2024 |
| 藤原ダム貯水池 | Gunma | 7.0 µg/L | — | 4.0 m | 2025 |
| 赤城大沼 | Gunma | 17 µg/L | — | 3.8 m | 2024 |
| 須田貝ダム貯水池 | Gunma | 7.0 µg/L | — | 3.7 m | 2024 |
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