You could measure do with an expensive device, but it’s
better to learn to analyze the conditions that impact do – for
better or worse – to predict bass location, which we’ll cover
later in the article.
Oxygen in the Water
oxygen diffuses into the water in several ways. it diffuses
through air/water contact on the surface – i.e. wave action, cur-
rent, etc. (which is also how the aerator in your livewell increas-
es the oxygen). it’s also created as a byproduct of photosynthe-
sis by underwater plants – grasses such as hydrilla and milfoil,
as well as phytoplankton in the water column.
Water conditions determine how much oxygen the water
can hold as well. colder water has more oxygen-holding capac-
ity, and water at lower altitude has the ability to hold more oxy-
gen. Water at its maximum oxygen capacity, which varies accord-
ing to temperature and altitude, is called “saturated.” do also
changes seasonally due to weather patterns and stratification.
More Oxygen Equals More Bass?
Much like you’d do if you walked into a room where you
couldn’t breathe, bass and baitfish avoid areas with low oxy-
gen, and you should consider this factor when on the water.
You don’t need a fancy meter or device to measure do, either.
Just know what to look for.
areas cut off from current (if there’s no plant life), areas with
dying vegetation (the decomposition process is oxygen con-
sumptive) and extreme depths in summertime usually offer
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sub-optimal do levels, and bass will generally avoid them.
same goes for some areas with a heavy algae bloom. turnover
in late summer can bring water with low do to the surface, too.
in contrast, areas with water running in or current – wind-
driven or natural – and green vegetation offer sufficient oxy-
gen levels. this can be particularly important in the fall and
winter when dissolved oxygen levels drop due to decomposi-
tion, hence the old saying “find the last green weeds in the
fall and you’ll find the fish.” the bass are there because the
green weeds contribute to higher oxygen levels in the sur-
rounding water.
When it comes to do, measuring the actual amount is sec-
ondary to understanding and recognizing how it affects a fish-
ery and where fish will be located. if you can recognize places
of low do that bass typically avoid, you’ll be ahead of the game.
FISH KILLS
low dissolved oxygen levels often contribute to local-
ized fish die-offs. these can be caused by oxygen deple-
tion due to ice cover, which doesn’t allow additional oxy-
gen to diffuse from the air. low do can also become an
issue after an excessive algae bloom in eutrophic or
highly productive waters. in such a situation, do levels
initially spike due to all the photosynthesis, but then
rapidly drop to unhealthy levels as the algae decompos-
es, absorbing the do along the way. ■
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