Everybody likes to keep cool. And that goes double for your pond fish. Cool water keeps your fish vibrant, healthy, and--surprise, surprise--alive! Fish, which are cold-blooded creatures, adjust their body temperatures to the ambient temperature of the water they find themselves inhabiting. When the water gets too warm, the fish overheat and may eventually die.

Even if they don’t, overly warm ponds make it tough for plants to grow and thrive, meaning your pond’s oxygen levels are likely to begin falling off, placing added stress on your fish. Warm water also encourages the growth of algae, which compounds the problem.

If that weren’t bad enough, warm water is a perfect environment for a wide range of parasites, diseases, and unfriendly bacteria--three of your fishes’ worst enemies. Anything over 80 degrees F. could spell trouble.

Thankfully, ponds rarely warm to that temperature overnight. At least that’s true with large, deep ponds. Smaller ponds and, particularly, pre-manufactured molded black vinyl ponds are prime candidates for overheating more quickly.

The best way to tell if your pond’s water temperature is approaching the danger point is to use an aquarium thermometer, one designed to be submersed in water. Another sure-fire sign that your pond is overheating is when your fish congregate near the surface, gasping for oxygen. Since warm water holds less oxygen than cool water, fish in a warm pond often end up starving for air.

If Your Pond Overheats

If you suddenly awaken to the fact that your pond is nearing the danger mark, there are several steps you can take to correct the problem.

1. Add some shade. Depending upon the layout and size of your pond, you can cover the 70 percent of the surface with a tarp. Or plant a row of trees or tall shrubs on the southern and western side of the pond.

2. Put up a baffle made from mesh or other material to help diffuse the sun’s rays before reaching the pond.

3. Drain up to 30 percent of the pond and replace it with cold water. If your water is heavily chlorinated, be sure to use a dechlorinating chemical. If your water supply contains chloramines (chlorine and ammonia), as an increasing number of municipal water supplies do, be sure to use a water-treatment product effective against that.

4. Increase the circulation of your water by increasing the size of your pump to one that pumps at least 3,000 gallons an hour.

5. Increase the aeration of your pond by adding a fountain or a spillway.

Of all the things you can do to help keep your pond cool during the dog days of summer and into fall, providing increased water circulation and shade are the two most efficient. Where I live in the high desert of southwestern Utah, we use a pump in combination with a stream and several spillways--plus a good deal of shade plants--to keep things cool and haven’t lost any plants or fish since doing so.

If you’re putting in a new pond in a warm climate, remember to make it deep enough so that at least part of the pond will always be cool. Heat rises, so providing your fish with a shaded area of the pond at least two feet in depth will provide them with an oxygen-rich environment and safety from predators, such as raccoons and migratory waterfowl. The deeper area will also cool warmer surface water as it circulates throughout the pond. Staggering your pond’s depth from shallow to deep will also allow you to plant a wider variety of water plants and marginals, from marsh pickerel, cattails, and cypress to water lilies and lotus.

Make sure to have plenty of pebbles and stones in the bottom to help create a good bacteria-friendly environment, which in turn will reward you with a healthy, vital home for both fish and plants.

Just remember to monitor your pond’s temperature regularly so that you can make adjustments before the temperature becomes critical.