On winter fish kills

One of the negative phenomena on the water bodies of Belarus causing significant damage are fish kills – mass fish mortality resulting from a decrease in dissolved oxygen in the water.

In winter, reservoirs and watercourses are covered with a thick layer of ice, which cuts off atmospheric air supply to the water, leading to a sharp decrease in oxygen content, without which fish cannot survive.

Fish kills are observed both as a result of a complete cessation of oxygen supply from the air and a sharp limitation of plant life under the ice.

In some fishing grounds, the bottom of which is covered with sapropel or other organic residues, pre-fish kill phenomena may be observed, associated with a drop in oxygen concentration below permissible limits (less than 4 mg/l).

An increase in the oxidizability of water to oxygen may also indicate a significant accumulation of oxygen-consuming organic matter. During thaws, agricultural runoff can be a cause of organic matter accumulation. High levels of ammonium nitrogen in the water indicate the presence of decomposition (rotting) products, further oxidation of which may be accompanied by a decrease in water oxygen content and the occurrence of secondary pre-fish kill phenomena.

In accordance with the Rules for Fishery Management and Fishing, approved by Decree of the President of the Republic of Belarus of July 21, 2021 No. 284, measures to prevent fish kill phenomena and eliminate their consequences are carried out by local executive and administrative bodies, or by legal entities specially authorized by them, and in fishing grounds leased or used free of charge – by lessees or users of such grounds.

To prevent fish kill phenomena, measures aimed at increasing the dissolved oxygen content in water may be carried out:

1. Liming of water bodies. Liming promotes the decomposition and accelerated mineralization of organic matter, as well as improves the gas regime and neutralizes the acidic reaction of water.

2. Making ice holes on water bodies prone to fish kill phenomena. The number of ice holes depends on the water body area and averages 3-5 per hectare. Ice holes should be located in the center of the water body and along its perimeter, where the depth of the unfrozen layer is 50-60 cm. To prevent ice holes from freezing over, it is necessary to install sheaves made of reeds, cattails, and other hollow "breathing" plants in them.

3. Aeration of water bodies. Aeration is the process by which air comes into close contact with water, by spraying water into the air or by passing air bubbles through water. In addition, an aeration method is used that utilizes hydromechanical mixing of the water column.

4. Hanging bags of salt in such ice holes.

We ask concerned residents of the Rossony district to assist aquatic inhabitants during this difficult time for their health.