Each year, especially those with extreme temperature changes, I get a number of pond owners call who have had a pond “turn-over”, with dead fish the end result. The weather we have been experiencing over the past few weeks, cool then hot, then cool again, have had some pond owners experience foul odors, murky water and dead fish.
It is oxygen depletion that is the cause of the most serious problems, especially the dead fish. Here’s how these turn-overs happen.
During hot summer weather, surface water becomes less dense as it absorbs heat and floats over a cooler, more dense layer of water. This layer prevents the oxygen produced in the warmer layer from mixing with the lower cooler layer. Since these two layers may not mix for weeks at a time, especially in deeper ponds, oxygen is eliminated near the bottom of these ponds.
Biological and chemical activities that take place in the lower, cooler layer is what uses and depletes the available oxygen. Next, a cool snap or a thunderstorm with wind and hard rain can cool the warm surface water making it heavy enough to sink and mix with the oxygen deficient bottom layer. The net result is a dilution of the oxygen and an increase in the demand for oxygen from dissolved minerals and decaying organic matter.
To complicate these problems –the algae usually die at the same time. When a die-off occurs, the green water often becomes streaked with gray, black or brown. The color of the water may eventually become totally brown, gray, black or even milky. A distinct foul smell may also be noticeable, often like rotten eggs. “Turn-overs” cause the most catastrophic fish kills in ponds, with 100% losses.
Some ways to help avoid this problem.
First, keep the nutrient level down so that plankton blooms don’t become excessive. Risk of turn-over is considerably less when visibility of a white object (disc) in the pond is 16-18 inches. You can hook a white object like a large pickle jar lid to a stick and mark the stick off in inches. This can be used to check the water.
Secondly and very helpful is the installation of an aerator that can be run at night and during extended periods of cloudy days. An aerator is good insurance against fish kills. An area of oxygenated water near the aerator will help the fish survive until the pond recovers from a low oxygen period.
We recently experienced a 100 kill off of fish in the pond behind our house.
Are the characteristics of a pond turn over the same as what happens when herbicidal growth inhibitors are sprayed directly into a pond?
Our community is in the midst of this discussion, as a chemical spraying took place at 7:30am last Friday, and by 2:00pm that day dozens of fish started dying off. By that evening 100’s of fish were dead and by the next day everything was dead.
The pond is shallow, 8 ft deep at the center, approx. 250yards long and 40 yards wide. We are in N.Virginia and have had continued high rainfalls for a month, which has kept the water running nearly continously.
There are now 100’s of dead small fish/minows stacked up at the far end of the pond, pushed there by the winds. No signs of any life.
Is the die off from pond turnover that fast/dramatic?
Hugh, What a terrible thing to have happen.
You ask-
The symptoms of a pond turn over is increased organic matter floating in the pond, milky colored water and a bad smell. Unfortunately, if fish were present, they would also be found gasping for air or floating soon after the event.
The organic matter and the milky water comes from the debris that is brought up from the bottom of the pond when the gases are released.
The gases formed in anaerobic conditions trapped under the debris at the bottom of the cause the sulfur or “rotten egg” smell of the ponds when they are released.
If you are referring to plant growth regulators being sprayed in the pond, we are not familiar with any PGR products that are labeled to be used in an aquatic environment. That is not to say that there aren’t any, but my research does not show anything.
In the case of herbicide poisoning, I would not expect to see changes in the ponds water. Most herbicides do not affect the appearance of the water unless they are designed specifically to do so. Algae control products which turn a pond a dark color to inhibit light entering into the pond are one exception. Some herbicides turn water a milky color, but I have not seen these particular products used in aquatic environments.
You should immediately contact the proper authorities and the company that did the application. You should also take immediate water samples, as well as samples of the fish and plants in the pond to have them tested.
Please keep us informed of what you discover so others can learn from the experience. Perhaps you can prevent this from happening again.
Our pond turned over today for the first time in 5 years. We have so far lost 25 catfish that were 20 to 30 inches long. My husband recently put in a blue die and it turned the pond a deep color to kill the alge. I think that this is what caused the oxygen depletion. What do you think? We have a foutain aerator. I think it is more for looks than a true aerotor. What should we do differently? The pond is 50 feet by 35 feet and about 6 feet deep in the middle.
Your pond is in the size and depth range that pond turnovers occur most frequently. Ponds that are 5-6 feet deep or more, allow for different temperatures in water, that is the upper and lower, or warmer and colder stratus to form more easily. Generally speaking, shallower ponds have a more uniform temperature range from the waters surface to the bottom, than deeper ponds. This lessons the chance of water layering, and causing inversions.
Your pond turning so soon after the dye was added shows that you already had a bad situation on the bottom of your pond. Although the addition of the dye may have not been a direct cause for the oxygen depletion, it could have been what initiated the pond turning. Pond dyes are known to change the water temperature of the pond causing the inversion, or water from the cold layer to move upwards into the warm water zone that has been holding it down, releasing the “bad” gas-hydrogen sulfide. This gas and others starve the water of oxygen, preventing any animal life in the pond from getting enough oxygen also, and they die.
Your use of an aerator is always very helpful, but I rarely recommend fountain types of aerators, unless they draw from the bottom of the ponds.
There are types of lake aeration systems I feel are most efficient.
The first uses an air diffuser that rests on the bottom of the lake/pond and is attached to a small air compressor resting on the bank by the way of a weighted air hose.
The second is a unit that floats on the waters surface and shoots a jet of aerated water down into the pond, to a depth of 2-8 feet. This unit agitates the ponds bottom, aerating the bottom so that the aerobic bacteria and small animals can degrade the debris.
In both cases the addition of pond bacteria is very important. I have read many studies where bottom organic sludge can be decomposed by up to two inches a month! Many times, ponds that were scheduled to be dredged, or drained and cleaned out, were saved from this major expense by aerating and applying bacteria.
Before any treatment is done on any body of water, it is always best to have a water test done to see what the nutrient levels are, as well as measuring pH etc.
Email us and I can recommend the systems we use. We will have the product pages on our site set up soon.
You mention an aeration unit that floats on the waters surface and shoots a jet of aerated water down into the pond. I have not found anything like that in online searches. Could you please tell me more? Is it something you sell? Thanks in advance for the info.
I have a 2 acre pond, mostly 10 feet deep. I believe this is what happened to me last night during a thunder storm in north east Nebraska. Thousands of fish have died! Yes thousands! I was at pond last night and noticed the fish where not eating as much as the days before. I didn’t think much of it because it was raining a little at the time. Then it stormed pretty hard last night and thousands of fish were dead in the morning. And thousands of fish were at the top 2 inches gasping for air. I got some aereators (water pumps and trash pumps) running as well as some air compressors running. The water pumps I had sucking off the top 2 feet and shooting into the air, and landing back into the pond. Then I took 2 air compressors and pumped air into the bottom of the pond. I also now( the next night) have a big stirrator at the top 1 foot shooting water into the air. I’m not sure if I’m doing this correctly? What would you recommend? How long do I need to run the aereators? The pond is spring feed from a 1/4 mile away. We own most of the ground that drains into the pond. No chemicals have been added to ground recently. We also have lots of healthy frogs in the area so I don’t think it could have been s chemical issue. I ordered an O2 tester off eBay tonight. What are healthy O2 levels? What depth do I measure them? What else do I need to keep an eye on? All day we were taking dead fish out of the pond. How long does it take for all of them to float to the top? Should I buy some sterile alge eating carp? If so how many?
Jake, it is almost impossible to predict a pond turnover event. Sorry to hear your losses were so high!
One of my clients had a pond that turned a terrible grey color every year. It looked like the inside of vaccuum bag mixed into his pond. You could not even see inches deep. Once we set up an aeration system, over four years ago, he has not lost a single fish and the pond is crystal clear to the bottom.
The trick is to get balanced aeration to the bottom of the pond to break up that inversion layer where the warm water holds down the cold water. On deeper ponds, this can be quite a task, but the overal health of your biological system will also increase if you can do it.
With proper aeration you will notice an increase of water clarity and a decrease of the build up of debris in the bottom of the pond. This will also increase the oxygen load of all aquatic zones.
It is great that you bring up the fact that no chemicals have been used in the immediate area. Many believe that insecticides are the most serious run off issue in our environment, but herbicides and disease prevention products such as fungicides can also be toxic to not only plant life, but also to fish.
As far as how long to keep the aerators running- there is no rule to follow. If electrical costs are of a concern, you can cycle the equipment to run for several hours and off for an hour. But turnover can happen any time of day or night. The O2 tester can be great help.
Usualy aquatic life losses are immediate when the conditions for low oxygen present themselves. If you are aerating properly, the fish that have not been overly stressed to this point, should recover.
As far as the sterile carp are concerned. This will have to be considered on a case to case basis. The carp are working great in one of the first ponds I consulted on, but not recommended on another where the aquatic grasses have not become an issue, but the bluegills and other panfish have been doing a great job. The carp would affect the smaller fish spawning beds in this particular pond.
You local ag extension agent or pond professional will be more qualified to provide detailed answeres.
Have fun just hanging out around the pond. After finishing a project, I can lounge around for hours just enjoying the beauty of a pond, large or small.