Russian men photographed wonders, and thousands of fish were frozen in the ice. How did this happen?

From the local weather, we may see some clues. It is reported that Norilsk, a city in northern Siberia, Russia, is affected by extremely cold weather, and the lowest temperature in some suburbs even reaches MINUS 55 degrees Celsius. Cold even forced primary and secondary schools to suspend classes for three days. It is estimated that this great cooling caused thousands of fish to be frozen in the ice. It is reported that fish come to this lake to lay eggs. They should have returned to the river through the dam water pipeline before winter came, but the pipeline was demolished a few years ago and the fish were trapped here.

In the news, the pipeline of the dam is an important channel for fish migration. After being demolished, the fish had no way to return to the river and could only freeze to death. Originally I laid eggs for the next generation, but I didn't expect to die here. Therefore, we need to know the dual effects of dams, that is, dams may also block the passage of fish in rivers. Fish, shrimp and crabs in the river need to move up and down at some stages of spawning, foraging and life. After the completion of the dam, the passage of aquatic animals was blocked, threatening their survival. The existing fishways and other facilities for passing fish cannot effectively ensure the necessary activities of fish, and it is very likely that some species will be endangered or even disappeared. Moreover, the bait of aquatic animals such as downstream fish is mostly carried by upstream water flow. After the completion of the reservoir, most of the water, sediment and bait are deposited in the reservoir, and the lack of food in the downstream fish may reduce production.

Dams are built in the upper reaches of rivers to meet the needs of power generation, water supply and irrigation through water storage. When storing water, little water is discharged, which often causes the river to be cut off, especially for inland rivers. For example, the lower reaches of the Tarim River have become more short of water because of the construction of reservoirs in the upper reaches, and the lower reaches of the Haihe River basin have basically dried up all the year round. In winter, the surface water temperature of the reservoir decreases, and when the water temperature is 4℃, the water density at the bottom of the water storage area is the highest. As the temperature rises in spring, the surface water temperature rises and the density decreases. When the water flow is small, the temperature stratification phenomenon of high water temperature and low water temperature occurs, which makes the bottom water temperature low all the year round. The low-temperature water released by the reservoir for agricultural irrigation will reduce crop production, and the decrease of river water temperature will also affect fish spawning and reduce catch.

In spring, the water temperature is low and the temperature rises gradually. If there is heavy rainfall at this time, the turbid runoff in the soil erosion area will enter the reservoir area, and the water temperature of the ground inflow is higher than that of the reservoir area. These turbid runoff will be suspended in the water surface of the reservoir area for a long time and cannot sink. Turbid water blocks sunlight, which affects the photosynthesis of aquatic plants and the growth of fish.