What is a primary concern when aquatic herbicides are overapplied?

The primary concern when aquatic herbicides are overapplied is hypoxia in water bodies. When herbicides are used excessively, they can lead to the rapid decomposition of treated aquatic plants. As these plants die and decompose, oxygen is consumed in the process, which can result in reduced dissolved oxygen levels in the water. This condition, known as hypoxia, can be detrimental to aquatic life, including fish and invertebrates, as they depend on sufficient oxygen levels to survive.

While water pollution from excess chemicals is a significant concern, especially in terms of broader environmental impacts, it doesn't directly link to the immediate biological effects that hypoxia does. Increased growth of unwanted weeds is not a direct consequence of herbicide overapplication but rather a potential issue from underapplication or resistance. Alteration of water temperature is not typically a direct result of herbicide applications; it is more influenced by physical changes in the environment. Thus, hypoxia is the most pertinent immediate threat connected with overusing aquatic herbicides.