Fish Kill Causes

Classifying fish kill events by their cause is a delicate balance between being accurate enough to be useful, but not so specific that similar events cannot be related to one another. The following categories are currently used to group fish kill events by cause.

Unknown

The exact cause of the kill is unknown. This may be due to several factors, including delayed reporting/investigation, weather events, and environmental conditions. Unknown causes may further be broken into those of suspected Natural origin or suspected Human/Anthropogenic origin. The comments for a particular kill may provide more information as to possible or suspected causes.

Disease/Parasite/Stress

This category is classified as a Natural Origin kill, and includes fish diseases, viral, bacterial, and fungal infections, various parasites, and spawning stress.

Environmental

Kills of this type occur due to environmental conditions not directly caused by human activity. Included in this category are temperature extremes, summer/winter kill, water stagnation from lack of flow, low dissolved oxygen, and general algal blooms.

Ammonia/Fertilizer

Anhydrous ammonia, land applied fertilizers (except animal wastes).

Animal Waste

Kills related to animal waste entering the waterbody. Further parameters are recorded if known.

Chlorides/Road Salt

Chlorides in runoff, usually associated with application of road salts and brine solutions.

Chlorinated Water

Typically from water main repair work or fire hydrant flushing.

Cyanobacteria Bloom

Toxins associated with a cyanobacteria bloom.

Gas Bubble Disease

A phenomenon typically found below dams at the large reservoirs (for example, Saylorville Lake and Red Rock Lake). Gas bubble disease occurs when levels of dissolved gasses (primarily nitrogen and oxygen) become supersaturated in a waterbody and in the blood of fish living in that waterbody. If a sudden change in river level prevents fish from reaching sufficient depth to keep the gasses their tissues and blood in solution, the gasses can come out of solution and form bubbles under the skin, in fins, and in the mouth. Hemorrhaging in the affected areas and exophthalmia (or “pop eye”) are conditions commonly associated with gas bubble disease. Fish mortality results from gas bubbles forming in the circulatory system of fish and blocking the movement of blood.

Mechanical/Electrical

Kills related to mechanical devices or electrical current in water.

Organic Material

Milk, silage, corn syrup, processing by-products (blood, tissue, eggshells, etc).

Other Chemical/Pollutant

A pollutant not listed, but not common enough to warrant its own category. If enough occurrences for particular pollutant occur, it may be assigned its own category.

Pesticides/Herbicides

Agricultural chemicals and urban lawn care products, not including fertilizers, typically used for pest control.

Petroleum Products

Oil, fuels (diesel, gasoline, etc), grease, lubricants.

Pollutant - Unknown/Unspecified

This category is used when the kill is caused by a pollutant, but it is unknown which particular pollutant. This is also used when the original report was unspecific as to what pollutant caused the fish kill.

Storm Water

A generic category for storm water runoff. These include but are not limited to general urban runoff during a storm event, warm water after a storm entering a cool/coldwater stream, causing thermal shock to coldwater species, and soil/material runoff from intense storms.

Waste Water

Human wastewater from lagoons, storage facilities, or private septic systems that experience malfunction or failure