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3.  Some structures and dams provide barriers to the migration of fish and
other aquatic animals, often necessary for feeding, spawning, and coloni-
zation purposes.
In addition, the aesthetic qualities of modified channels are generally poor,
thereby reducing recreational use potential. Temporary storage of pollutants
within the stream channel is also minimized, thereby increasing the first flush
pollutant load effects on downstream receiving waters. These factors indicate
that habitat improvement techniques, in addition to water pollution control
measures, may need to be implemented to satisfy fish and aquatic life objectives
within these channelized stream reaches.
The basic approach to improving the biological potential of a modified stream
channel is to: 1) provide protective areas where a suitable sediment substrate
may at least temporarily accumulate; 2) increase vegetative growth; and 3) elim-
inate barriers to aquatic animal migration. Table A-3 presents a description of
selected measures which could be used to increase the biological potential of
existing and future modified channels. In addition to providing suitable habitat
for aquatic life, stream channel rehabilitation enhances the aesthetic qualities
of the stream and--through temporary sediment storage, aeration, increased
shading, and biological nutrient uptake--improves the water quality of the             I
stream. It is recognized that most of these rehabilitation measures by their
nature decrease the hydraulic efficiency of the stream channel. However, in many
cases the hydraulic efficiency could be maintained at a level which would not
preclude achievement of flood control design. A site-specific study would be
required to determine the potential of each stream reach to provide biological
habitat and at the same time be acceptable for flood control purposes.
LAKE REHABILITATION MEASURES
The reduction of nutrient inputs to lakes in southeastern Wisconsin, while
preventing further water quality deterioration, may not necessarily result in the
elimination of existing water quality problems.    The indicated water quality
improvements expected from a reduced nutrient input will be inhibited or
prevented by conditions which include, for example, in eutrophic lakes, the
presence of continued mixing or an anaerobic hypolimnion (the lower layer of a
stratified lake), which may release significant amounts of phosphorus from the
sediments to the overlying water column.   Similarly, rooted aquatic plants may        I
continue to grow prolifically in nutrient-rich bottom sediments, regardless of
the nutrient content of the overlying water.      If this occurs, or if other
characteristics of a lake result in a restricted water use potential, the
application of lake rehabilitation techniques should be considered.
Lake rehabilitation techniques that are applicable to southeastern Wisconsin
include dredging, sediment covering or consolidation, nutrient inactivation,
hypolimnetic aeration, and total aeration.      Other techniques, perhaps more
properly classified as lake management practices, would include macrophyte
harvesting or chemical control, algae chemical control, and fish management. The
applicability of experimental techniques, such as biological control, selective

discharge, algal harvesting, dilution/flushing, and inflow treatment, requires
additional study. Many of these techniques require federal and/or state permits
to be issued prior to implementation. A brief description of lake rehabilitation
techniques is set forth in Table A-4.
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