Ponds fulfill a lot of roles in Georgia. They provide water
for thirsty crops and
livestock. They offer a cooling dunk for people and animals. And
they (sometimes
reluctantly) give up their fish for a summer fish fry.

It’s no
wonder they run short of something.

“During the dog days of summer, we see many ponds become
oxygen-depleted,”
said George Lewis, an aquaculture and fisheries specialist with
the University of Georgia
Extension Service. “Pond owners may need to aerate (add
oxygen to) their ponds to
ensure the pond stays healthy.”

Most bodies of water that cover less than 15 acres are ponds,
Lewis said. Anything
larger is a lake. Both can become oxygen depleted, but smaller
ponds are more at risk.

“Ponds tend to be warm through their entire depth. Lakes
probably have a layer of
cooler water near the bottom that can hold enough oxygen to
support the life in it.”

Ponds likely to become oxygen-starved include those near
areas where a lot of organic
material is on or in the ground or where fertilizer is used
heavily.

This includes not only pastures with livestock and many farm
fields, but areas around
golf courses or manicured suburbs, too.

“Animals that graze around a pond add a huge amount of
organic waste to the
water,” he said. That waste can deplete the oxygen
faster.

Ponds with lots of fish are good candidates for oxygen
depletion, too. Fish use a
surprisingly large amount of oxygen.

Lewis said the oxygen isn’t depleted in just one or two days.
Hot, hazy days in late
July and August are the most likely time the problem will start.
The water is warm, so it
holds less oxygen. The sun isn’t shining directly into the pond
so phytoplankton aren’t producing as much oxygen.
And the bacteria and fish in the water need more oxygen.

“Everything is right for less oxygen to be
produced,” Lewis said, “when
in fact, the pond needs more oxygen.”

Oxygen depletion usually happens slowly over four or five
days before obvious symptoms
appear. The first symptom is usually the water changing color to
a bright green. Another
sign is a fairly sudden increase in fish deaths.

Whatever symptoms appear, Lewis said, the visibility in the
water shows the oxygen
level. Put something white or shiny under the water. The oxygen
is probably about right if
you can see the item 12 to 18 inches deep.

“Visibility of less than 12 inches points to potential
oxygen depletion,” he
said. “You may need to aerate the water before your fish
start dying.”

Lewis said night aeration provides the best oxygen source for
ponds. During the day
phytoplankton, microscopic plants in the water, produce oxygen
through photosynthesis.

At night, the sun isn’t providing the light the plants need
to make oxygen, so the animals in
the water slowly use it up.

“That’s
why you’ll find
the lowest oxygen levels in a pond just before sunrise,” he
said. “When the
problem is getting serious, you’ll see fish at the surface
literally gulping air.”

Pond owners use many methods to aerate their ponds. Lewis
follows a rule of thumb for
aerators of one horsepower per surface acre. Anyÿsystem
that breaks up a water stream
into small droplets falling into the pond should oxygenate
well.

It’s
impossible to aerate a pond too much, he said. The oxygen
dissolves in the water. When the
water is holding as much as it can, no more will dissolve into
it.

“Not all ponds will need aeration during the
summer,” Lewis said. “But
if a pond needs oxygen, it needs it quickly.”