Aquatic Insects - Sitka National Historical Park (U.S. National Park Service) Insects and other macroinvertebrates serve as indicators of the health of our rivers and streams. How does this work? Certain organisms require high levels of dissolved oxygen (found in clean, healthy streams) to survive, and others thrive in lower levels of dissolved oxygen (found in more polluted streams). So, by looking at the insects surviving in the ecosystem, we can determine the relative oxygen levels, and therefore the health of the system.