Poisonous hot spring water

...Off the coast of Japan, it is expected that undersea hot springs will be discovered in areas of high crustal heat flow on the seafloor west of the Ogasawara volcanic island arc.
[Poisonous hot spring water]
When acidic springs and hydrogen sulfide springs gush out in large quantities and flow into rivers, they inhibit the growth of the flora and fauna in the rivers and also make it impossible to use the rivers for agricultural purposes, so they are called hot spring poison water. At Kusatsu Onsen, 5,000 liters of sulfuric acid acid spring water (pH 1.5) flows into the Agatsuma River every minute as the Yukawa River, causing the pH of the river water, which was neutral upstream, to drop to 3-4, causing problems for agriculture, fishing, forestry and flood control projects, and hydroelectric power generation.

*Some of the terminology that refers to "toxic hot spring water" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…日本近海では，小笠原火山島弧西側海底の高地殻熱流量地帯に海底温泉が発見されるものと期待されている。
【温泉毒水】
　酸性泉，硫化水素泉などが大量に湧出し，河川に流入すると河川中の動植物の発育を阻害し，河川の農業用の利用もだめになるので温泉毒水と呼ばれている。草津温泉では毎分5000lの硫酸酸性泉(pH1.5)が湯川となって吾妻川に流入し，このため上流で中性であった河川水のpHは3～4に低下し，農業，漁業，治山治水事業，水力発電に障害を与えていた。…

※「温泉毒水」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報