Some reservoirs are more than ten or twenty meters deep, with a large temperature difference between the water surface and the bottom. Even on a hot summer day, the water temperature at the bottom can still be freezing, and "cold puddles" can easily form. Cold water puddles are usually located at particularly deep places under the water and are always static and motionless. If a swimmer encounters a cold puddle, he or she will get cramps no matter how good the water quality is.

In summer, more people go swimming in reservoirs, and drowning accidents have also entered a period of frequent occurrence. Among them, teenagers and children are prone to drowning accidents due to their weak awareness of safety precautions and lack of self-control.

Disadvantages of reservoirs

1. Increase the frequency of disasters

The construction of reservoirs may induce earthquakes and increase the frequency of earthquakes in the reservoir area and nearby areas. Reservoirs in mountainous areas will have an increased frequency of landslides, collapses and debris flows as the lower parts of the mountains on both sides will be immersed for a long time in the future.

2. Cause sedimentation in the reservoir area

Due to the interception by the dam, the slowdown in water potential and the backwater in the rear area of ??the reservoir, sediment will inevitably accumulate in the reservoir, especially the dam. and siltation at the end of the reservoir (effect of backwater).

3. Salinize the soil

Continuous irrigation also raises the groundwater level, bringing the salt in the deep soil to the surface, plus the salt in the irrigation water and various High levels of chemical residues lead to soil salinization.