What is the most common reason for herbicide-related fish kills?

The most common reason for herbicide-related fish kills is the lowering of dissolved oxygen. When herbicides are applied, especially in larger quantities, they can lead to the rapid growth of aquatic vegetation. As this vegetation decays, the decomposition process consumes significant amounts of oxygen from the water, which can create hypoxic (low oxygen) conditions. Fish and other aquatic organisms rely on adequate dissolved oxygen levels to survive; when these levels drop significantly, it can lead to stress and ultimately death for the fish in that environment.

Water contamination, incorrect dosage, and the presence of toxins can also contribute to fish kills but are not as commonly related to herbicide applications specifically. Contamination can occur through various pathways and is not exclusive to herbicides. The incorrect dosage might result in reduced effectiveness rather than direct harm to fish populations, while the presence of toxins typically refers to other pollutants or chemicals not associated directly with herbicide use. Consequently, the lowering of dissolved oxygen stands out as the primary mechanism leading to fish kill incidents related to herbicide application in aquatic environments.