Extreamly hot weather caused thousand of fishes dead

In the early of Auguest, the weather in Taiwan is extreamly hot. Continuously hot weather and low water level caused the teperature of river water getting high and high. Then, many fishes happened a lack of oxygen sympton. They did not swim in the riffle water, just stay in the shallow and peachful water. Even I came close; they still did not take any move. I observed their eyes and found that their eyes were with red colour. I guessed they would not be alive soon.

Every year this kind of things happen again and again. Does it mean this is a nature disaster or human-made disaster? Lack of enough vegetation and plants, the rivers very easily become flooding when the flooding season comes. Instant heavy raining cause the speed of water getting into the river too fast just because no tree can stop the rain drop for a while. This problem makes the water flowing speed faster; then, it will also bring the mud and sand flood later.

Reconsidering this problem, this disaster is natural or human-made.....