nutrient Levels
Reservoirs can be classified by their
nutrient load, and fisheries biologists
have several terms to summarize the
average productivity and nutrient load
found in a body of water. this is called
the reservoir’s trophic state.
oligotrophic reservoirs are low in
productivity. they contain cold, highly
oxygenated clean water relatively
devoid of nutrients. they have low
plankton loads, low abundance and
diversity of aquatic vegetation, and host
the smallest fish biomass. lake Mead is
an example of an oligotrophic reservoir.
eutrophic reservoirs feature high
productivity, high nutrient loads, high
levels of plankton, abundant aquatic
vegetation, and the highest fish bio-
mass, to a point – as they can get so
nutrient laden that they actually
become toxic to fish of all species,
resulting in fish kills. Ross Barnett is a
eutrophic reservoir.
Mesotrophic reservoirs are a blend
between the two, featuring moderately
clear, cool waters with good oxygen lev-
els, and ample plankton and aquatic
vegetation production. they host abun-
dant fish populations and are often
some of the best fishing reservoirs year
in and year out. Kentucky lake is a
mesotrophic reservoir.
think about the trophic state when
you are preparing to fish a reservoir. if
you’re fishing a more oligotrophic
reservoir, it’s probably best to go with
realistic finesse presentations. if you
know it’s eutrophic, concentrate on
techniques you’re comfortable with in
dark water and aquatic vegetation.
nutrient load isn’t the only way
anglers can classify reservoirs, howev-
er. timber, or the lack thereof, is anoth-
er key component of reservoir type.
Whether a reservoir was clear-cut prior
to impoundment plays a huge role.
for example, famed Missouri/
arkansas border impoundments Bull
shoals and table Rock lake are known
for acres of deep-water standing timber
– and the excellent fishing they offer.
lesser-known norfork lake is on
the north fork River not far from Bull
shoals. in all other respects, except for
size, it is a similar reservoir to Bull
shoals and table Rock. however,
norfork was clear-cut prior to flooding,
and as such contains significantly less
deep-water cover and is not consid-
ered nearly as good a bass factory as
Bulls shoals and table Rock.
this doesn’t mean timber is essen-
tial to bass fishing success in all places,
but among similar reservoir types, the
presence or absence of timber can
certainly be a key factor in bass loca-
tion and abundance.
Generally, if a reservoir is devoid of
timber, bass can be found around shal-
low cover or in vegetation.
reservoir use
another important way to classify a
reservoir is by its purpose, whether
electrical generation or some other
purpose, such as flood control, drink-
ing water or irrigation.
Bass and baitfish populations in
power-generating reservoirs can be
more dependent on current flow for
Mesotrophic
positioning than those in reservoirs
where there is irregular or less consis-
tent current flow.
if you know a reservoir generates,
dam operators usually publish genera-
tion schedules online. periods of high
flow often coincide with some of the
best fishing.
if it’s just a flood control dam, pay
more attention to the recent rain condi-
tions, as runoff is the only source of cur-
rent. Keying in on even small sources of
inflow can lead to more success.
invasive
Game-Changers
introduce an invasive
species into the reservoir equa-
tion, and it can dramatically
change the way the lake fishes.
in several reservoirs of the
carolinas, the introduction of
blueback herring in the 1970s
and 1980s created an almost
unique type of reservoir, where
the majority of the fishing effort
in postspawn revolves around
chasing bass gorging on the
pelagic bluebacks.
pay attention to the forage
base in your local reservoir, and
any bulletins provided by your
state’s fisheries managers. if
you’ve got bluebacks, rusty
crayfish, eurasian water milfoil
or any of a host of other inva-
sives, you might want to consid-
er how it will impact your fish-
ing strategies. ■
Eutrophic
Oligotrophic
a clear-cut case?
The trophic state of a reservoir determines its productivity and ability to support biomass.
january 2018 I fLWfIshInG.com
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