Kills and Spills Team
Clues to Common Causes of Fish Kills
| Large fish die (all types)
Small fish still alive
|Low Dissolved Oxygen||Kills often due to hot weather with algal blooms.
Fish are seen "gulping" for air at the surface in morning.
Dead fish are found in the morning.
Dead fish are often white in color and floating.
|Small fish die (all types)
Large fish still alive
|Toxins: metals, pesticides, herbicides, fertilizers, and chemicals.||If the chemical amount is large, all fish die.
Effect on fish varies by chemical.
|Only one type of fish dies||Diseases||Often all the fish are the same size.
Most often it is 10 days after a weather disturbance.
|Typically virus||All the fish died within 1 or 2 days.|
|Typically bacteria||All the fish died within 5 to 10 days.|
|All types and all sizes of fish die||Acute Stress||Weather made water too cold or too hot.|
|Fish die after cold front||Temperature||Water temperature too cold.|
|Fish die in shallow water with temperature over 100||Temperature||Water temperature over 100°F.|
|Fish die and water clear when it would normally be very green.||Very low dissolved oxygen or toxins||Large amounts kill all living organisms.|
Any type of fish that has "fuzzy white patches" has fungus. Fungal infections are secondary after some primary cause of stress. Stress can range from cold or hot temperatures, breeding stress, cuts, parasites, lack of sufficient food, high or low flows, or any other factor that stresses a fish or creates internal or external damage. Fungal infections usually appear 7 to 10 days after damage or stress occurred.
Always notice odors, water color, and water clarity (how far you can see into the water). Can you see the bottom? How far down can you see?