Copper is most toxic to fish in?

Copper is most toxic to fish in soft water due to the lower concentrations of calcium and other minerals that would typically bind to copper ions, reducing their toxicity. In soft water, the lack of these minerals enhances the bioavailability of copper, meaning that it is more easily taken up by aquatic organisms. The reduced hardness in soft water allows copper to have a more pronounced negative impact on fish by interfering with physiological processes, potentially causing stress, gill damage, and even mortality. Understanding the relationship between water hardness and copper toxicity is crucial for effective aquatic weed control and protecting fish populations.