True or False: Black flies are primarily found in heavily polluted waters.

Black flies are not primarily found in heavily polluted waters; rather, they thrive in clean, rapidly flowing water sources such as streams and rivers. They require high levels of oxygen, which is typically abundant in unpolluted water. Heavy pollution reduces the oxygen content and affects water quality negatively, making it unsuitable for black fly larvae, which depend on specific water conditions for development.

In contrast, while black flies can be found in various environments, their preference for clean and well-oxygenated waters differentiates them from organisms that thrive in polluted conditions. This preference is crucial to their lifecycle and habitat requirements, reinforcing the correctness of the assertion that they are not predominantly associated with polluted waters.