Look at the chart below. We know that the water in Dwyer Lake is polluted because of the presence of sludgeworms. In this case, sludgeworms are a... what?

In this context, sludgeworms are typically considered bioindicators of pollution. Bioindicators are organisms whose presence, absence, or abundance reflects the health of an ecosystem or a particular environment. The presence of sludgeworms in Dwyer Lake suggests that the water is polluted because these organisms thrive in environments with high organic matter and poor oxygen levels, often resulting from pollution sources such as wastewater discharge or nutrient runoff.

The presence of sludgeworms indicates that the water quality is compromised, as they can tolerate but do not thrive in clean, healthy environments. Environmental scientists often use these organisms to assess the overall health of aquatic ecosystems, making sludgeworms a critical element in evaluating the biological integrity of Dwyer Lake. Therefore, in this case, sludgeworms are indicators of water pollution.