Fish ponds certainly add tranquility and interest to a backyard, but caring for a pond can be more work than expected.

Fish pond temperatureCredit: Wikimedia Commons: Biofilter tech


When keeping koi fish and other large fish outdoors, the pond water temperature must be maintained according to what those fish need to survive. In some regions, the climate may be ideal from winter to summer, allowing the pond water to remain at just the right temperature year round. However in areas where summer time highs regularly hit 90 degrees F, or in winters with below freezing temperatures, maintaining the fish pond temperature takes more effort than just leaving it up to nature. This is especially true if you are keeping the most common pond fish koi. Koi are very tolerant when it comes to temperature changes, but freezing temps and extremely hot summers can be too much for them.  

Summer Care: Keeping the Fish Pond Temperature Cool

Keeping your pond from getting too hot in the summer starts with the design phase. The more water your pond holds, the more time it takes for the summer sun to heat it up. Build a pond that measures at least five feet across along one length and is at least four feet deep. A large volume of water will have more consistently cooler water temperatures throughout even tpond waterfall filterCredit: Amazonhe hottest summer months. Also, install a waterfall or filter that keeps the water moving at all times. This gently mixes the water so that the entire pond remains at the same water temperature and hot spots do not form.

Landscape in and around your pond to provide shade to the water. Aquatic plants such as water lilies and water lettuce will shade the water directly. Small trees and vines growing on trellises around the pond will provide shade intermittently throughout the day. Shading will also help control algae growth and deter predator fish such as herons.

In climates with extremely hot summers, you will need to take more measures to keep your water cool. You may need to add or build a permanent gazebo, arbor or other decorative structure that sits directly over the pond to provide shade from sunrise to sunset. Another option is to use a blue pond dye that reflects sunlight away from the water.

Winter Care: Keeping the Pond Water Temperature Warm

Many of the steps needed to care for a fish pond in the summer also help winterize a pond. Build a large pond so that during freezing temperatures the entire volume of water does not turn to ice. Use a waterfall feature or filter to keep the water moving and less able to freeze.

In some regions, the above steps are all that is necessary in keeping a fish pond from freezing. However, in areas where temperatures remain below freezing for extended periods, electroFish pond de icerCredit: Amazonnic heating becomes necessary. Several types of water heaters are available for ponds. Some heaters sit outside the pond. Water cycles from the pond, through the heater, then back into the pond. There are also pond heaters you can place directly into the pond itself. Some work by sitting at the bottom to heat the water. Others de-ice the surface of the pond by floating at the pond surface. 

It’s best to consider your year round climate when you are just starting your garden fish pond project. Use this information to design elements of your backyard pond to make temperature control easier to accomplish. If you have a backyard fish pond already established, and found your pond does not maintain the ideal water temperature year round, it is not too late to make adjustments. By adding features such as landscaping, waterfalls and heaters, you can it more resistant to extreme temperature fluctuations.