Name one common indicator species for polluted freshwater.

Caddisflies, specifically from the order Trichoptera, are commonly used as indicator species for assessing water quality in freshwater ecosystems. They have a wide range of sensitivity to pollution, with different species displaying varying tolerances. Many caddisflies thrive in clean, unpolluted waters, making their presence a strong indicator of healthy aquatic ecosystems. Conversely, a significant reduction or absence of caddisflies can signal declining water quality due to pollution.

In addition to their sensitivity, caddisflies play an essential role in the food web and are valuable for scientists conducting biological assessments of freshwater environments. Their life cycles often involve larval stages that inhabit the substrate, where they can accumulate pollutants, thus providing insight into the level of contamination in their surrounding environment.

While salmon and trout are also important fish species, their presence is not as definitive an indicator of pollution because they can sometimes tolerate a range of habitat conditions. Biodiversity of aquatic plants can reflect water quality as well, but it does not provide as specific a measure of pollution as caddisflies do, which can quickly indicate changes in water quality due to their distinct ecological requirements.