The term benthic is given to organisms that live at the bottom of a body of water. More than 300 benthic species live at the bottom (are part of the sediment) of the St. Clair River. Three such species are pictured below.
If an absence of a species having low pollution tolerance is observed, this may indicate a pollution problem. Note – Rapid water flow, a rocky bottom, etc. often account form smaller populations of benthic organisms.
Benthic Organisms Have Differing Tolerances to Pollution
The population size of Mayfly Larvae relative to that of the Aquatic Worms indicates the health of the sediments.