Slide 63 of 75
Notes:
A number of researchers have documented that at about 10% impervious cover, the aquatic insect community in urban streams begins to decline sharply. Studies conducted in Delaware, Maryland, and Washington document this relationship. One typical change in the aquatic community is the change in composition from stone flies, mayflies and caddisflies to a community of worms, midge larvae and snails, e.g. more pollution tolerant organisms.
Hellgramites (also known as "toe biters") are sensitive to alterations in stream habitat brought on by urbanization and can be part of an indicator-based assessment of stream quality.