What does a mass presence of midges typically indicate about the water quality?

A mass presence of midges is often viewed as an indicator of poor water quality or pollution. Midges, particularly the larvae, thrive in environments with high levels of organic matter and nutrients, which can result from pollution. When water bodies are enriched with excess nutrients, often due to runoff from agricultural practices, sewage discharge, or other pollution sources, midge populations can explode as they are able to feed on the decaying organic material that thrives under these conditions.

While nutrient levels are crucial for midge growth, high nutrient levels alone don't inherently imply a healthy ecosystem. An excess of these nutrients can lead to eutrophication, which can deplete oxygen levels in the water, harming other aquatic life forms. Therefore, the significant presence of midges, particularly in large swarms, is generally taken as a sign that the ecosystem is imbalanced and potentially suffering from pollution or poor water quality.