The fish are mostly carp.
Thousands upon thousands of fish have washed ashore dead in Lake Khatyng, in the Sakha Republic, located in the coldest regions of Russia. Locals in the area, blame government officials who have been dynamiting rivers which connect to the lake, to ease the massing of ice dams to prevent eventual flooding. The government admits to using explosives to control the icing problems, but denies that the fish are dying because of this. For one thing, the dead fish do not appear to have any visual external damage.
Others in the area feel the oxygen levels have diminished to lethal levels under the ice due to the extreme winter temperatures that have plunged to 122 degrees below zero. This seems like the more logical explanation. Fish do need oxygen to survive, and some species need more than others, or they cannot adapt as well as others to the depleting levels, for reasons that are not fully known. Carp prefer warmer temperatures when breeding, the ideal temp. is 32F. (It is believed that they are not the best at adapting to lower levels of oxygen caused by freeze-outs). When winter conditions persist, ice thickens, and snow builds up, thereby diminishing the oxygen supply below; the supply can only last for so long. Shallow lakes are the most vulnerable. If these conditions persist for too long, a “winter-kill” occurs and fish die. Some experts believe that this is part of the evolutionary process and actually fosters a quicker and stronger growth rate for the surviving fish.