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What Is This Indicator, and Why Is It Important?
This indicator reports on “biological integrity”—the
degree to which the suite of fish and bottom-dwelling animals
in a lake or stream resembles what one might find in a relatively
undisturbed lake or stream in the same region. Tests assess
the number of different species, the number and condition
of individuals, and food chain interactions for fish and bottom-dwelling
(or benthic) animals, which include insects, worms, mollusks,
and crustaceans. High scores indicate close resemblance to
“natural” conditions, and low scores indicate significant
deviation from them.
Undisturbed lakes and streams in a particular region have
a relatively predictable set of fish and bottomdwelling animals,
which occur in predictable proportions. Alterations to the
stream or lake can change the composition and condition of
these biological communities from this undisturbed or “reference”
condition. Alterations that affect biological integrity include
decreased water quality, introduction of non-native species,
changes in the amount or timing of water flows, and modification
of the lake or stream bed or shoreline. Some lakes and streams
are so modified that, for example, both the number of species
and the number of individuals are very low when compared with
undisturbed areas, and many of those that remain are diseased
or otherwise damaged. Ecosystems that are “healthy,”
or show high integrity, are more likely to withstand natural
and man-made stresses.
Why Can't This Indicator Be Reported at This Time?
The tests of biological integrity now in use have been developed
primarily for streams and wadeable rivers; methods for lakes
and larger rivers are not as well developed. In addition,
these tests must be tailored to each region of the country
to ensure that each stream or lake is compared with an appropriate
reference. Only a handful of states regularly conduct quantitative
tests of the condition of fish or bottom-dwelling animal communities.
Thirty states are developing such tests, and five states already
use such tests in regulating water quality.
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