Three-inch thick carpet of algaeic "fluff"
on sand bottom of Sebago Lake, Long Point area, Standish, August 1997. Long-time
lake residents remember this area as having a clean, rippled sand bottom
prior to the 1990s. Photo by Sonny and Helen McAlpin, Underwater Photo &
Video.
4. Analysis of impacts of lake-level management on fish populations
of Sebago Lake.
Studies suggest artificial lake regulation can adversely affect fisheries
and wildlife.
Water level charts since 1872 indicate that a sustantial amount of interannual
variability occurred prior to 1987. The average annual hydrograph prior
to 1987 tended to mimic that which would occur for an unregulated lake.
Since 1987, Sebago Lake has been highly and unnaturally regulated.
The major change in dam operation since 1987 has had the following results:
a higher and stable water level throughout the growing season, change of
the seasonal timing of peak, and a substantial unnatural drop in lake levels
during the winter months. FOSL believes the fisheries of Sebago Lake have
been adversely impacted by the licensees operation of the dam. FERC (1997)
agreed with FOSL's contention that the effects of lake-level regulation
on Minnesota's Rainy Lake can be compared to similar issues at Sebago Lake,
stating: "These water level regimes [for Rainy Lake] are generally
consistent with the various water level regimes proposed for Sebago Lake."
A 1998 review of the International Joint Commission's Order for Minnesota's
Rainy and Namakan Lakes stated:
"The recent modelling exercise with respect to natural (unregulated)
lake levels has confirmed that both lakes have been markedly altered as
habitat for fish. Changes have been wrought in lake levels per se, in the
timing of lake level maxima and minima, and in the amount of variability
pertaining to both lake levels and the timing of hydrological events. The
greatest changes in absolute terms have been manifested in reduced lake-level
variability." p.26.
"... the further the water level declines in the growing season, the
more the littoral zone habitat would be affected. Supporting documentation
shows a well developed littoral area forms the base of the food web and
the system is driven by base habitat conditions." p.30
Since Rainy Lake water level management is compared to Sebago Lake one could
expect similar ecological impacts to become evident.
" ... The key to proper management of these lakes lies in optimizing
water level control during the summer months. The habitat would be vastly
improved by allowing more dramatic water level changes during this period."
p.30
Regarding regulated lakes in Finland, Hellsten (2000) wrote: "Water
level regulation in northern lakes constitutes a typical environment problem
... At the first stage following the beginning of regulation, the ecological
changes are often noticed only by local fisherman as changes of fish stocks."
FOSL questions whether recent declines in the populations of native Sebago
Lake salmon and rainbow smelt are have been caused entirely by the introduction
of non-indigenous lake trout (Salvelinus cristivomer). FOSL recognizes that
landlocked Atlantic salmon (Salmo salar), rainbow smelt (Osmerus mordax)
and many other fish species have difficulties on regulated lakes even in
the absence of non-indigenous lake trout.
Investigations by FOSL suggest the Songo River Delta has changed in recent
years from a ripple sandy bottom to algaeic aquatic macrophyte carpeted
substrate. Instead of a sandy substrate, the littoral floor consists of
a highly siltated substrate. In these FOSL comments, other ecosystem components
are discussed with significant interconnectivity between the fishery and
littoral, wetland, and tributary impacts from unnatural water level regulation.
FOSL emphasizes that it is the interconnectivity of many habitats and the
geomorphological and ecological alterations that is crucial to understanding
the impacts of water level regulation on the lake fishery.
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