Ponds & Streams
Cold Winters Hard on Pond Fish: What You Can Do
COLUMBUS, Ohio — Long, cold, snowy winters, like this year’s, can lead to big fish kills in ponds. But there are steps you can take to help fish survive, said an expert at The Ohio State University.
The key is a pond’s oxygen level, said Eugene Braig, aquatic ecosystems program director in Ohio State’s College of Food, Agricultural, and Environmental Sciences.
“Many game fishes become stressed when dissolved oxygen concentrations fall below 5 parts per million,” said Braig, who works in the college’s School of Environment and Natural Resources. “Very few fish species can tolerate dissolved oxygen concentrations of 2 ppm or less.”
The problem is, without intervention, the oxygen level in ice- and snow-covered ponds can drop from 8 ppm or more at the start of winter to 1 ppm toward the end — curtains for bass and bluegill, for example. Here’s what Braig suggests.
If you’ve never installed a pond aerator, such as a bubbler, then shovel off some of the snow from the ice. Try to clear 25-50 percent of the pond’s surface — provided, as a rule of thumb for safety, that the ice is at least 4 inches thick, he said.
How it helps: Shoveling some of the snow lets in sunlight. Plants and algae still living in the water below can resume their photosynthesis. The process adds oxygen to the water.
Run a bubbler
If you have installed a bubbler, run it whenever ice starts to form, ideally from shallower depths. When the pond is ice-free, turn it off. Another option is running an air stone, which produces clouds of very small bubbles.
How it helps: Bubblers and air stones infuse oxygen into the water, which helps both in winter and summer. They also roil the water surface and so keep holes in the ice. There, oxygen in the air will diffuse into the water, which likewise raises the oxygen level.
Raise your bubbler
In winter, raise your bubbler so it’s not on the bottom, where it normally sits in summer. Elevate it to about 2 feet below the surface of the water. Or move it to shallow water. Set an air stone, too, about 2 feet deep.
How it helps: By raising a bubbler or air stone, you limit circulation of the water column. The deep water stays deep, the shallow water, shallow.
In summer, mixing those waters is a plus. But in winter it can hurt. It brings up and chills down the relatively warmer deep water, where fish often ride out the worst of the cold. Without this refuge, with nowhere to go but into mixed-up, all-frigid water, a fish’s stress goes up. So does its risk of turning belly up.
But don’t both shovel and bubble
Pick one practice or the other, Braig said — either shovel or aerate, but don’t do both. “Aerated ice,” he said, “is not likely safe enough to support a person’s weight to allow snow removal.”
Hope for a thaw, even a short one
Even in wicked winters, a warm spell can thaw a pond for a few days, according to “Winter and Summer Fish Kills in Ponds,” a fact sheet by Ohio State University Extension, the college’s statewide outreach arm.
“Oxygen levels quickly rebound when a pond becomes ice-free,” the fact sheet says.
“One timely warm period of two to three days can greatly reduce the possibility of a fish kill.”
Manage aquatic plants and algae
Managing aquatic plants and algae starts when you first dig the pond, Braig said. The shoreline should have a 3:1 slope, or 3 feet of run for 1 foot of drop. This limits the area of shallow water, where summertime plant growth can boom.
In an existing pond, use chemical, mechanical and biological controls, if and as needed, to keep aquatic plant growth in check.
“Given their valuable function in producing oxygen, there’s a value in managing an appropriate coverage of aquatic plants,” he said.
“Depending upon your management goals for the pond and its fishery, having up to 25 percent of the surface area in plant cover is probably appropriate.”
How it helps: Having the right coverage of aquatic plants contributes to more stable oxygen levels through photosynthesis, he said.
Also, managing for limited plant coverage serves to limit how many plants will eventually die and decompose. Decomposition uses up some of the oxygen in the water — sometimes lots of it — and can lead to too-low levels in winter. Less rotting of dead plants means more oxygen for fish.
Start with a deep enough pond
Braig said in Ohio the recommendation is for 25 percent of a pond’s area to be more than 8 feet deep, and in the northern part of the state, the same percentage to be 10-12 feet deep.
How it helps: “Ponds with a greater volume of water potentially have a greater reservoir of dissolved oxygen and tend to be less susceptible to winter kill,” he said.
To learn more about preventing winter fish kills, Braig suggests these sources:
“Winter and Summer Fish Kills in Ponds,” go.osu.edu/FishKills.
“Controlling Filamentous Algae in Ponds,” go.osu.edu/ControllingAlgae.
Ohio Pond Management Handbook, wildlife.ohiodnr.gov/portals/wildlife/pdfs/publications/fish%20management/Pub432.pdf.
Much of the information in this story came from the winter 2014 edition of Braig’s online newsletter, Your Pond Update, senr.osu.edu/YourPondUpdateWI2014.
Spring Pond Management
Now that spring is here, it is time to control the weed issues you may have experienced last year. Vegetation is not a bad thing in ponds. Aquatic plants add necessary food and oxygen to the aquatic life that reside in your pond. Some of the good weeds are under the water’s surface and are not a visual issue. It is the vegetation on top of the pond’s water that can cause so much anguish. The first issue to typically appear (and the one that frustrates pond owners the most) is not a weed at all, it is Filamentous algae.
Filamentous algae is a fibrous mat that looks ugly when floating on the pond’s surface and seems to appear overnight. This alga starts its growth cycle on the pond’s bottom. As it grows, it builds oxygen under its fibrous mat. Once buoyant it floats up to the surface. At first, a couple mats will appear and within a few days, the entire pond surface can be covered. It looks bad and if you use your pond for swimming, it is gross to walk/wade through. Fishing can become annoying when the algae snags on the fishing line and hook each time you reel in the line. A little bit of this menace can lead to some major headaches. Left unchecked, it can explode into a real issue that is bad for the pond.
Of course, the next question is, “How do I kill it?” The time to treat for Filamentous algae is when it is growing on the bottom of the pond. Once it floats to the surface, it is too late to treat as it is already dying. Filamentous algae is controllable with some effort. Management needs to be a multi-front approach including mechanical, chemical, biological, and structural control strategies to reduce and rid the pond of this unwelcome guest.
Once the algae floats to the surface there is no sense to treat it with chemical as it is already dying. The best strategy is to mechanically remove it with a rake by pulling it out of the water and away from the pond. You can also drag a rake on the pond bottom, close to shore, to break up the mats making them come to the surface quicker to remove them from the pond. The best time to do mechanical removal is on a windy day as mother nature will help you by blowing the floating algae to one area, making for easier removal. Do not leave the removed mats on the pond bank. As it dies, the nutrients flow back into the pond aiding to the next cycle of growth.
Many copper-based chemicals work very well on filamentous algae. Again, once it comes to the surface it is a waste of money to treat then. Chemical application works best after physical removal of mats, both floating and on the pond bottom. Following this order will require lower volumes of costly chemicals and lessens the potential of killing fish. When treating a pond with any chemical only treat a quarter of the pond at once. If you treat and kill all the plants at the same time, you can create a very low dissolved oxygen zone in the water. It takes large volumes of dissolved oxygen to break down the now dying or dead organic matter. Robbing the water of its dissolved oxygen starves the fish of oxygen and can lead to their death.
Biological and Structural Strategies
This is the hardest one to work on as it often means changing what is happening on the land around the pond. Adding more White Amur fish (biological) is not the answer. They eat bottom rooted pond plants, not algae. If runoff from the landscape runs into the pond this can be a source of nutrient loading. If you do not stop the source of nutrients getting into the pond, then it will be hard to get ahead of the algae. Reducing the pathway (structural) of nutrients getting into the pond will help greatly.
One thing that helps all ponds is the use of an aerator to add oxygen to the water column. Especially in ponds that are trying to breakdown organic material that robs oxygen from fish. Two types exist; the best method is a bottom bubbler (called a diffuser) that forces air from the pond bottom up to the surface with a series of fine bubbles. The other is a fountain. Although they look nice, they do not do as good of a job getting the oxygen back into the water column. Wind and fresh water flowing into the pond will also add a little oxygen, but if the incoming water is laden with nutrients, then it is just adding to the weed and algae growth.
Lastly, keep the Canada Geese off your pond. They are neat to look at, but they are dirty, annoying, and just a couple can really throw off the water quality (especially in small ponds). Their manure, which they deposit at the ponds edge, (where you walk) is very high in phosphorus. Soluble phosphorus is the nutrient that best grows algae. A mature goose at 14 pounds of weight defecates more than 28 times a day, depositing 2 pounds of high nutrient goose droppings. Plus, if you let two geese take up residence, the next year you will have more, as many of the offspring will stay.
Most pond owners would probably agree that having clear water adds to the aesthetics of their pond. The clarity of pond water is primarily influenced by the abundance of microscopic plants (phytoplankton), animals (zooplankton), and suspended soil particles. Phytoplankton and zooplankton abundance will influence the water clarity to varying degrees depending primarily upon the time of year, time of day, and fertility of the pond. Generally, these tiny plants and animals do not influence water clarity as significantly as suspended soil particles.
Muddy water is the result of tiny soil or clay particles suspended in the water. Muddy water can have negative effects other than detracting from the aesthetics of the pond. Muddy water can hinder the feeding ability of largemouth bass, bluegills, and redear sunfish and even reduce their growth. Additionally, phytoplankton growth and abundance is reduced in muddy water. This may compound the problem of poor fish growth in muddy ponds by reducing the amount of food available through the entire food chain.
The first step in correcting a persistent problem with muddy water is to determine the cause. To do this, collect a jar full of pond water, cover it with a lid, and allow it to sit undisturbed for one week. If the water appears clear after one week and sediment is noticed at the bottom of the jar, chances are that something in the pond is stirring up the sediments. However, if the water is still cloudy, then there is a good chance that suspended particles of clay soil are the cause of the muddy water.
The problem may also be a combination of disturbed sediments and the presence of clay soils in the watershed. If disturbed sediments are determined to be the problem, one or more of the following suggestions may help remedy the situation:
Remove undesirable rough fish from your pond. Bullheads and common carp have a habit of rooting around in pond sediment while feeding. Channel catfish may also cause the same problem.
Fence livestock away from the pond and avoid pasturing them on the pond’s watershed. Livestock trample and compact pond banks, causing them to erode.
Establish moderate vegetative growth of rushes, sedges, and cattails to protect pond banks and shoreline areas from wave erosion.
Keep domestic ducks and geese away from the pond. Their feeding activity may destroy shoreline vegetation and resuspend soil particles from the pond bottom.
Maintain good vegetative cover throughout the watershed. If you do not have ownership of the entire watershed, then establish buffer strips of vegetation around the pond.
Plant windbreaks to prevent wind from causing excessive wave action and disturbing sediment in shallow water.
These suggestions offer the best long-term protection against muddy pond water. It is much easier and cost effective to prevent soil particles from eroding into a pond than it is to remove them once they become a problem. If the previous methods prove unsuccessful, it is likely that the muddy water problems are caused by colloidal clay particles that stay in suspension for a long time. Since colloidal clay particles do not settle out easily, other techniques are necessary to improve water clarity. Several techniques are effective at removing colloidal clays from pond water. Each technique requires the addition of various materials to the pond that cause clay particles to settle out. These additives include organic matter (hay), aluminum sulfate (alum), calcium sulfate (agricultural gypsum), and hydrated lime. Each of them work through a chemical reaction that causes suspended clay particles to clump together. These clumps of particles are heavier than individual articles and therefore sink rather than stay suspended. Most of these additives can be purchased from local agricultural supply stores.
ODNR Division of Wildlife - Ohio Pond Management HandbookChapter 6: Page 33