– Written by International Sales Manager, Joe Holz
As we head into the cold, winter months, protecting your fish should be on your top priority list. Many pond owners understand the need to have good oxygen levels to maintain a healthy, thriving fish population, however, most only think about oxygen levels during warm, summer months. Winter oxygen levels in areas that ice over can be just as, or even more, critical than during warmer times of the year. Low oxygen levels and the buildup of harmful gases over the winter can create dangerous conditions for fish in your pond.
Ice Cover, Fish and Plants
Once a pond ices over in the winter, only small amounts of new oxygen can be introduced to the system. Some plants may be able to survive as long as snow and ice cover doesn’t block the sunlight and they will give off some oxygen through photosynthesis. However, that amount is often limited and can stop altogether if snow cover blocks most or all of the sunlight.
Metabolism of fish and other pond inhabitants does slow in the cold water, limiting the demand for oxygen and preserving the oxygen longer than during warm water. Lower demand can prolong the life in the pond, but long winters or ponds with high fish populations can create critical situations as winter drags on. Decreasing oxygen levels can be deadly for fish. If levels drop low enough, fish health can suffer and may eventually die.
Harmful Gas Buildup
Often just as deadly and just as common is the issue with the buildup of harmful gases. While biological processes slow, they do not stop altogether. The byproducts such as CO2, methane, sulfur compounds, etc. can build up to toxic levels if they are not allowed to vent out of the water into the atmosphere.
Keys to Protecting Your Fish
Your best defense to prevent these winterkill situations is to keep and maintain a small, open water area. The WI DNR suggests as little as 1-2% of the surface area needs to be kept ice free to prevent winterkill. Simply opening a small area will allow enough life sustaining oxygen to absorb into the water. Cold water has the ability to hold a lot of oxygen, much more than warm water. Equally as important is the ability for harmful gases to vent off into the atmosphere.
Most ponds or lakes are best served with diffuser systems to maintain open water. Placed near deep water is best and the average open water area is roughly 3 ft. in diameter for every 1 ft. of depth of diffuser placement. Best practices also include keeping the diffusers close enough to shore to maintain open water right next to land. This is for safety of people, animals or pets that could fall into the open water. If water is open up to the shore, they can simply walk out. It’s also a good idea to post warning signs near open ice or even fence off the open area.