Why fish die on the Volga: an analysis of the causes and consequences

Mass loss of aquatic biological resources in the basin of the Volga River in the current season is recorded mainly in water areas with a slow current and a high level of anthropogenic load, which indicates the complex nature of the environmental disaster. The main triggers of smoke are a sharp decrease in the concentration of dissolved oxygen in the water and a simultaneous increase in the toxicity of the habitat due to industrial effluents. Visually, this process is manifested in the surfacing of huge schools of bola, bream and perch, which do not have time to leave the contaminated areas due to paralysis of the respiratory system or shock.

The situation is aggravated by the fact that the natural mechanisms of self-cleaning of the river, such as aeration and the activity of saprophytic bacteria, do not cope with the volume of incoming pollution. In the hot summer months, when water temperatures rise above critical levels, the rate of oxygen consumption by biological objects increases, and the ability of water to retain gas decreases. It is the combination of these factors that creates a “perfect storm” leading to a large-scale frost, the consequences of which are felt not only by environmentalists, but also by local fishermen and residents of coastal cities.

Oxygen starvation as the main factor of freezing

Dissolved oxygen deficiency is the primary and most common reason fish die on the Volga, especially during summer heat and winter ice. Water heated by the sun, physically loses the ability to be saturated with oxygen, and the absence of wind and storm phenomena prevents the natural aeration of surface layers. In the bottom layers, where organic residues accumulate, rotting processes begin, which actively consume the remaining oxygen, creating oxygen-free zones that are deadly to hydrobionts.

The situation is especially critical in the areas of discharge of warm water from hydroelectric power plants and industrial enterprises, where the temperature regime is artificially violated. Thermal pollution It speeds up the metabolism of fish, causing them to consume more oxygen, which is already insufficient in warm water. This leads to rapid depletion of the body’s energy resources and mass death of even large individuals, which are usually more resistant to environmental changes.

In winter, the mechanism of freezing works differently: the ice shell completely blocks the flow of oxygen from the atmosphere, and the rotting of aquatic vegetation under the ice finishes the remaining reserves. In such conditions, the fish suffocates, and only emergency measures for cutting holes and installing aerators can save the situation, which is technically difficult to implement on long stretches of the Volga.

• 🌡️ Increasing water temperature reduces the physical solubility of gases.
• 🦠 The decomposition of organic matter (algae, wastewater) dramatically increases the oxygen consumption of bacteria.
• 💨 The absence of wind and mixing of water masses creates stagnant zones.
• 🏭 The discharge of heated water from CHPP and NPPs violates the natural thermal balance of the river.

⚠️ Oxygen starvation often occurs rapidly, and the fish does not have time to migrate to safe areas, dying in their permanent habitat.

Chemical pollution and industrial wastewater

The second major factor explaining why fish die on the Volga lies in the regular and emergency releases of chemicals by industrial enterprises. Despite the availability of treatment plants, their efficiency often does not meet modern environmental standards, which leads to the ingress of heavy metals, phenols, petroleum products and organochlorine compounds into the river. Even small concentrations of certain substances can cause death or chronic diseases in ichthyofauna.

Vulcan discharges that occur when ponds-sludges are overflowing or as a result of accidents on pipelines are particularly dangerous. In such cases, the concentration of toxins in water exceeds the maximum permissible norms by tens and hundreds of times, causing instant tissue necrosis in fish and paralysis of the nervous system. Toxicology analysis The dead fish often show the presence of mercury, lead and cadmium, which accumulate in the tissues, making the catch dangerous for human consumption.

Agricultural runoff containing fertilizers and pesticides also contributes to ecosystem degradation. Washing off the fields by rain, nitrogen and phosphorus enter the Volga, causing a rapid bloom of blue-green algae. When they die off, these algae release cyanotoxins, which are the strongest poison for most fish species, especially juveniles and sensitive species such as sturgeon.

Impact of climate change and temperature regime

Global warming has a direct impact on the hydrological regime of the Volga, making the habitat conditions of fish more extreme. The increase in heat waves causes the river to warm up to temperatures close to the upper biological survival limit for many species. Prolonged exposure to high temperatures causes heat stress, suppresses the immunity of fish and makes them susceptible to infections.

Climate change also affects the water level in the river: snow-sleeping winters and dry summers lead to shallowing of the Volga. Reducing water levels reduces habitat volume, increasing fish planting density and contaminant concentrations. Under such conditions, any negative factor, whether it is a small discharge or a short-term decrease in oxygen, becomes fatal.

Seasonal shifts disrupt the natural biorhythms of migration and spawning. Fish can spawn too early or too late when conditions are not yet or are no longer suitable for the survival of caviar and larvae. Phenotypic changesClimate-induced juveniles are born at a time when the feeding base has not yet formed, leading to their mass death from hunger.

Factor.	Impact on fish	seasonality
High temperature	Oxygen loss, heat shock	Summer.
icebreaker	Gas exchange lockdown, freeze.	Winter
Floods	Flushing pollution from land	spring
Drought	Toxin concentration, shallowing	Summer-Autumn

Biological Threats: Parasites and Diseases

Weakening of immunity due to poor ecology opens the way to various infectious diseases, which under normal conditions are controlled by nature itself. Outbreaks of ichthyofauna are often recorded in fish congestion sites where pathogens are transmitted by contact. Among the most common causes of the pestilence are viral hemorrhagic septicemia, rubella of fish and various bacterial infections.

Parasitic invasions also play an important role in reducing the population. Helminths that settle in the gills, liver and muscles of fish, disrupt their vital functions. With severe infection, the fish loses the ability to eat and breathe normally, becoming easy prey for predators or dying from exhaustion. Epizootic monitoring It shows that in recent years the virulence of some strains of parasites has increased.

Invasive species such as rotan or Chinese perch, imported by humans, displace native species and bring with them new diseases to which local fish do not have immunity. Competition for the feed base and direct predation by aliens further destabilize the ecosystem of the Volga, making it less resistant to external influences.

The Hidden Dangers of Invasive Species

Invasive fish species are often carriers of parasites and viruses exotic for the Volga. Once in a new environment, they not only displace native species, but also infect them with pathogens to which the natives do not have centuries-old immunity. This leads to cascading epidemics that cover vast areas.

The anthropogenic factor: poaching and dredging

Human activity causes direct physical damage to fish stocks, and poaching is a leading force. The use of prohibited fishing gear, such as electric rods, nets and nets, leads to the destruction of not only commercial fish, but also juveniles, which did not have time to give birth. An electrolyte maims a fish even if it does not die immediately, disrupting reproductive function.

The dredging work required for shipping is also contributing to the environmental disaster. The rise of sediments that have been accumulating heavy metals and toxic substances for decades leads to secondary water pollution. The exasperated silt creates clouds of suspension that clog the fish's gills, causing mechanical asphyxia. The most vulnerable are bottom fish species, such as catfish and sterlet, which are in direct contact with raised soil.

The construction of hydraulic structures and dams disrupts the natural migration routes of fish to spawning sites. Fish can not overcome artificial obstacles, accumulate in the lower biefas, where conditions are often unfavorable, and die from stress and poor water quality. Fragmentation of the habitat divides the population into isolated groups, which reduces the genetic diversity and resilience of the species.

⚠️ Note: The use of electric rods and nets during spawning is prohibited by law and is punishable by heavy fines and confiscation of equipment, but the scale of illegal fishing remains high.

Diagnosis and monitoring of the condition of ichthyofauna

To identify the causes of the pestilence of fish, specialists conduct a comprehensive diagnosis, including a visual inspection, hydrochemical analysis of water and pathoanatomical examination of dead individuals. It is important to respond quickly to signals from local residents and fishermen, as delays can have irreversible consequences for the entire ecosystem of the region. Environmental monitoring allows you to track the dynamics of changes and predict possible outbreaks of diseases or frosts.

Laboratory studies allow to determine the exact chemical composition of water and fish tissues, to identify the presence of specific toxins or pathogens. Based on the data obtained, measures are being developed for the rehabilitation of water bodies, which may include aeration, introduction of biologics or restriction of economic activities in the affected areas.

Public control also plays an important role in water conservation. Activists and volunteers help to clean up dead fish, prevent secondary contamination of water by decomposition products, and conduct public awareness work. Only by joint efforts of the state, science and the public can damage be minimized and the unique ecosystem of the Volga for future generations can be preserved.

Prospects for recovery and protection

Restoration of the Volga fish stocks requires a systematic approach and significant financial investments. It is necessary to modernize the treatment facilities of industrial enterprises and introduce waterless production technologies, which will minimize the discharge of contaminated wastewater. Regeneration Ecosystems are a long process, but with proper management, the first positive results can be seen in a few years.

An important area of work is the artificial reproduction of valuable fish species in fish farms. The release of young sturgeon, salmon and other species helps maintain the population, but without addressing the root causes of fish death, these measures are temporary. There is also a need to strengthen the monitoring of environmental legislation and to increase accountability for environmental crimes.

International cooperation within the Caspian basin also plays an important role, as the Volga flows into the Caspian Sea, and the problems of one part of the basin inevitably affect the other. Sharing of experience, technologies and monitoring data allows for the development of more effective strategies for the protection of aquatic biological resources.

Why do fish die in the summer?

In summer, two critical factors are combined: high water temperature, which reduces oxygen content, and the active reproduction of bacteria and algae that consume this oxygen. In addition, in the summer there is often calm, which prevents the mixing of water.

Is it dangerous to eat fish caught in the sea?

It's not recommended. Fish that died from suffocation or poisoning, quickly decompose, it accumulates toxins and pathogens. Even heat treatment does not guarantee the safety of such a product.

Can a regular fishing trip affect the situation?

Amateur fishing in permitted places and permitted gear does not cause critical damage. The problem is created by poaching methods (nets, electric rods) and non-compliance with catch norms, leading to the destruction of juveniles.

Where to report the mass death of fish?

Facts of fish pestilence should be reported to the territorial bodies of Rosrybolozhstvo, Rosprirodnadzor, the environmental prosecutor's office or by a single number of emergency services 112.