Why is it recommended to lower the water level when treating with rotenone?

Lowering the water level when treating with rotenone is recommended primarily because it decreases chemical costs. When the water level is lowered, the concentration of rotenone is effectively increased in the smaller volume of water. This can lead to more efficient control of unwanted fish species without needing to use larger amounts of the chemical, thereby reducing overall costs.

This practice ensures that the treatment is still effective while minimizing the financial impact on the application process. The other options may reflect benefits or outcomes of aquatic management strategies, but they do not pertain directly to the cost effectiveness of using rotenone in a concentrated manner through water level management.