Mother Nature and ponds

The last three weeks I have been “swamped” at work, considering I’ve been swamping around in farm ponds. I’ve seen everything from well-manicured and landscaped shorelines to huge slopes, the kind you can roll into the pond. I’ve seen some pretty clear water and then one that smelled like a sewer. The common theme is, people want good clean ponds for livestock, fishing and swimming and other recreational pursuits.

The main problems ponds have is too many weeds, too much algae, and not enough oxygen in the summertime. Depleted oxygen causes fish to die. To keep a pond healthy, you’ve got to do several things.

The first is to reduce weed growth by eliminating nutrient sources such as lawn or farm fertilizer, livestock manure, or septic tank leachate — the liquid produced by water trickling through the waste.

Pond weeds are a natural process, but we speed it up with fertilizer runoff. Autumn leaves are a double-whammy if you have trees around the pond. Falling leaves contain 60 percent of the nutrients a tree takes in during a year, he explains, so those nutrients now feed pond vegetation. In decomposing, leaves also take up dissolved oxygen, thus competing with fish for the oxygen supply. This results in more nutrients to feed even more pond weeds. Be sure to cut down trees that are on your dam. If they should die, the rotting roots can cause ponds to leak or weaken the dam. It’s a natural ecosystem.

Mother Nature wants plants in a pond. People don’t. There’s been a change in our mindset since the days of bullfrogs on lily pads. Now people want ponds to be like a swimming pool, with crystal clear water full of five-pound bass. But you can’t have both.

To eliminate the shallow water where weeds thrive, a pond should have relatively steep sides and good depth. A good slope is one foot down to every three feet across, and it is recommended that 25 percent of the pond be more than eight feet deep – both for fish habitat and weed reduction.

Oxygen depletion causes fish kills in summer because oxygen is less soluble in warm water, which is exactly when fish are most active and need more oxygen. Learn to spot the problem because if it’s serious, it’s immediate, and you have to act. You don’t have time to price-shop for an aerator.

We do have an excellent publication on Aquatic Weeds; you can find it on our online bookstore at


Jody Holthaus41 Posts

Jody Holthaus is the Meadowlark Extension District agent in the area of livestock and natural resources.


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