In environmental monitoring, which organisms are often used as simple, cost-effective indicators of water quality, especially in streams?

• A. Birds
• B. Fungi
• C. Macroinvertebrates
• D. Mammals

Answer: (C)

Biomonitoring relies on organisms that reflect the conditions of their habitat. In streams, macroinvertebrates—the small aquatic animals such as insect larvae, snails, crustaceans, and worms—are especially useful because different groups tolerate different levels of pollution and oxygen. They stay in the stream long enough to integrate environmental conditions over time, so their community mix and diversity provide a readout of overall water quality. They’re also inexpensive and straightforward to sample with simple nets or by kick sampling, making them a practical choice for regular monitoring. A stream with good quality typically hosts a variety of pollution-sensitive members like mayflies, stoneflies, and caddisflies, whereas degraded streams show fewer of these and more tolerant species, often with reduced diversity. Birds and mammals, while part of the ecosystem, move around and reflect broader landscape conditions rather than direct stream water quality. Fungi can indicate organic enrichment but aren’t as universally practical as a simple, cost-effective stream-quality indicator as macroinvertebrates.