09/11/2026
Seeing dead fish on the shore of your pond can be worrying, but should only be cause for concern if you see many at once.
Fish kills can occur for many reasons, but the most common is suffocation from lack of dissolved oxygen. After many consecutive warm, cloudy, and windless days, excessive vegetation can use more oxygen than it’s producing. Algal bloom crashes can also happen under these conditions, depleting oxygen. These crashes can be artificially induced by excessive herbicide use.
To prevent lack of oxygen, aerate throughout the whole summer and occasionally in the winter. Prevent excess nutrient and organic matter build up through creating a buffer zone, deepening shallow areas following a 3:1 ratio, and/or using herbicides sparingly.
Pesticides can also kill fish as well as other animals who use the pond. Symptoms usually appear within 24 hours of pesticide use. If you suspect a pesticide-related fish kill, call the New Mexico Environment Department (NMED) immediately. Make sure to read labels carefully, as many pesticides and herbicides are toxic to fish, including some approved for use in water.
Fish kills can also be caused by disease. These usually happen because the fish are already stressed by poor environmental conditions and/or overcrowding. Nothing can be done once the disease outbreak has happened, but stressful conditions can be avoided by taking proper care of the pond.
For more information, read full NMSU Extension publication, "Understanding and Preventing Fish Kills in Your Pond": https://pubs.nmsu.edu/_w/W105/index.html
