Reports of Winter Kills in Lakes and Ponds Coming in as Ice Melts

The calls come in about this time of year. Winter ice has melted
and a pond owner or early season angler heads down to check things
out. Dead fish? Not a good sign.

“I’m getting lots of calls. We had a fairly hard winter again
and people are calling about fish kills on ponds,” relays Scott
Gritters, fisheries management biologist for the Department of
Natural Resources. You can expect a few fish to die each winter.
However, a deep blanket of snow can mean problems. “Heavy snow-and
we had a lot of it through December into January—keeps sunlight
from penetrating through the ice,” notes Gritters. “That causes
algae in the pond to die back, which depletes oxygen.”

In Iowa, there are about 90,000 ponds. Most are farm ponds,
holding water from surrounding slopes or hillsides. They often
provide watering holes for livestock. A growing number of ponds are
showing up in towns, too; especially as developers and city
planners work to contain runoff.

Well managed ponds are excellent fisheries. A strong
zooplankton/insect base feed the bluegills or other panfish. Most
of them end up as dinner for larger predator fish. However, as
thousands of their siblings are consumed, the rest grow to decent
sizes; delighting anglers young and old. And with a good forage
base, those predators— largemouth bass for instance-hit trophy
sizes. Throw in some channel catfish, which aren’t choosy about
whether their food is still living, and you can develop a balanced
‘back 40’ fishery.

So now, after a hard winter, you have to assess the damage. “I
ask people to walk around the pond and see what kind of fish are
dead,” says Gritters. “If it’s mostly large fish, then the smaller
fish-which need less oxygen-might have survived. As they grow, they
should fill that big fish gap. If the shoreline is littered with
dead fish of different sizes then that indicates a widespread die
off.”

In that case, restocking may be your next move. Private
hatcheries and other commercial vendors—even some farm supply
stores—offer various fish stocking options. The DNR does as well;
though the pond stocking program revolves around that three species
combination. Young-of-the-year bluegill and catfish are shipped
early in the fall. By the next summer, largemouth bass are
available. The pond owner is charged $25 an acre for the stocking
and certain other requirements must be met; such as pond acreage,
depth and whether livestock are kept out. Information is available
at www.iowadnr.gov or by
calling your area fisheries biologist.

Oh, and to nip in the bud one of the most commonly asked
questions, ‘No, you do NOT have to let anyone fish in your pond
just because the DNR stocked it.’ But since angler license sales
help offset the cost of pond stocking, it is always appreciated if
pond owners do allow some angler access.

Of course, prevention is better than restocking. An inspection
of your pond can determine whether it is too shallow, or perhaps
whether it has too much nutrient-load or chemical runoff entering
it. Any of those factors can lead to problems.

If it is in good shape, the best prevention comes in the winter.
“A lot of people look at aerators for their ponds. That is a viable
solution,” says Gritters. “A cheaper method is just to scoop the
snow from the ice; to let light penetrate.” He admits, though,
repeated shoveling after each heavy snowfall can get old in a
hurry.

From there, as long as you don’t upset the balance in the pond,
lunker bass and hand-sized bluegills can be common. Biologists
usually advise setting up a catch and release policy for any big
bass. Some have to remain in the pond to eat into the forage base.
Otherwise, an overpopulation of stunted bluegills, for instance,
will appear. Likewise, catfish do not readily reproduce in such
confined settings and you shouldn’t take too many.

Maintain a balance in that pond-whether it is in a cattle
pasture or a subdivision-and the payoff will be great fishing
across four seasons.

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