9 Ways to Keep a Pond Cool in the Summer

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Garden pond in the summer
Significant increases in heat can be detrimental to your pond fish and plants. julie corsi / CC BY 2.0

Now that the days are increasingly warm, it’s high time to prep any outdoor water features for the compounded effects of extended daylight hours, increased temperatures, and potential water shortages. Though many types of ornamental fish, aquatic plants, and microbes do benefit from moderate warmth, their metabolic rates and overall survival may be compromised by significant increases in heat. Without protection, shallow ponds can quickly become inhospitable in hot weather!

Apart from stressing aquatic organisms and increasing their susceptibility to disease and reproductive issues, high summer temperatures can negatively impact the chemistry of pond water. If the water temperature is consistently kept above 29˚C (84˚F), the pond may experience reduced dissolved oxygen levels, an acceleration of nutrient release, and increased chances of algal blooms. As metabolic and chemical reaction rates increase in response to higher temperatures, oxygen depletion and pH fluctuations are also likely to occur.

Furthermore, high evaporation rates due to excess heat would lower your pond’s overall depth while enhancing the concentration of harmful solutes. Understanding these impacts helps implement strategies for keeping an outdoor pond cool. The tips below, when carried out before the onset of extreme heat, should help maintain your pond’s ecological balance through the season.

1) Grow a diversity of aquatic plants

Persicaria amphibia
Having a diverse selection of aquatic plants in your pond can help to increase oxygen levels, provide shade, prevent harmful nutrient buildup, and more! NobbiP, CC BY-SA 3.0, via Wikimedia Commons

Aquatic plants have far-reaching benefits that extend beyond their aesthetic contribution to both ornamental and wildlife ponds. A healthy diversity of native species should provide shade, facilitate evapotranspiration, increase oxygen levels, and prevent the buildup of harmful nutrients. Floating plants like water lilies and duckweed can create a green canopy that reduces sunlight penetration, while emergent plants like bulrushes and cattails cool the shoreline through transpiration.

Submerged plants, such as hornwort and anacharis, aid in nutrient absorption, preventing algal blooms. They also contribute to oxygen production in deeper parts of the pond, supporting aerobic processes that ultimately generate less heat. Apart from maintaining healthy water parameters, aquatic plants also open up microhabitats, which are, in turn, associated with their own microclimates. For example, the shade beneath large lotus leaves provides refuge for young fish and amphibians.

When narrowing down your selection of plants, keep in mind that the right species are crucial for effective temperature control. Not all floating or emergent plants can tolerate direct exposure to sunlight. Moreover, non-native species can exacerbate problems by disrupting ecological balance. Native plants are typically the best choice as they are adapted to your local environment and can thrive under the prevailing conditions.

2) Situate trees or shade structures along the pond’s perimeter

Trees along pond perimeter
Planting trees around your pond’s perimeter can help to ensure cooler water temperatures during the summer months. Elysse, CC BY 3.0, via Wikimedia Commons

Strategically planting deciduous trees or installing pergolas and shade sails around residential, public (in parks, for example), or agricultural ponds can maintain cooler water temperatures through summer. Their presence should provide consistent shade, which helps stabilize water levels. If you’re worried about having to clean up after periods of heavy leaf fall, consider planting evergreen species or go for non-living alternatives with some structural flair!

In residential and urban settings, these shading methods enhance the visual appeal and usability of ponds, offering spots for relaxation and community engagement. For agricultural ponds, shade structures help conserve water for irrigation and livestock. By choosing region-specific plants and adaptable shade structures, pond owners can manage water temperatures effectively, promoting healthier and more sustainable aquatic ecosystems.

3) Keep the pond water moving via aeration methods

Pond waterfall
Anything that can consistently disrupt the water’s movement helps to increase oxygen levels and improve circulation. Viking Visual / CC BY-ND 2.0

Aeration systems – pond fountains, waterfalls, air pumps, decorative spitters, and virtually anything that can consistently disrupt the water’s movement – introduce oxygen into the water and promote circulation. This facilitates heat exchange between the water and the surrounding air, aiding in the dissipation of excess heat from the water’s surface.

Submerged diffusers and pond pumps also help prevent thermal stratification and heat stress in deeper ponds. When these optimize dissolved oxygen levels, they support nutrient cycling by promoting the breakdown of organic matter, preventing algal blooms that would otherwise result from increased nutrient concentrations and warm temperatures.

A great way to enhance your pond’s aeration system, keeping temperatures down all through summer, would be to incorporate a biological filtration method. As water passes through filter media enriched with beneficial microbes, excess nutrients can be stripped as the constant circulation keeps the water cool.

4) Increase the pond’s depth

Koi pond
During hot days, fish will often remain closer to the pond bottom to try and keep cool. Wonderlane / CC BY 2.0

It’s a no-brainer that shallow water would either warm up or cool faster than deep water. Building or modifying the pond to have deeper areas, especially if you are located in a region with markedly warm summers, is a great way to maintain stable temperatures throughout the year. Deeper water layers, which collectively act as a thermal buffer, are less affected by surface heat. Thus, to alleviate the impacts of heat stress, your fish may remain closer to the pond bottom during hot days.

A pond depth of at least 3 – 4 feet is usually recommended for year-round temperature stability in temperate zones. Increased depth has multiple benefits. Deeper ponds can be designed to have complex microhabitats – each with varied trends in water circulation and light exposure. Habitat complexity supports a range of aquatic plants and animals, enhancing the pond’s overall resilience to seasonal fluctuations.

If you have a container pond and it still has room for more water in summer, consider maximizing the water volume. This should at least help mitigate the effects of evaporation. Lost water may then be re-supplied every few days to weeks. Make sure to constantly monitor the water depth; replenish lost volume before it drops to below the level deemed safe for your fish.

5) Conduct partial water changes more frequently

Pond water with leaves
During periods of high temperatures, try to replace 10 – 20% of an ornamental pond’s volume per week. Nikolaj Potanin from Russia, CC BY-SA 2.0, via Wikimedia Commons

Summer is a great time to pay more attention to your pond. As the days are warm and long, you might find yourself with a surplus of bright, daylight hours – perfect for outdoor maintenance work! Dedicate a few hours per month to conducting more frequent water changes. During stretches of intense heat, aim to replace 10 – 20% of an ornamental pond’s volume per week. Water changes dilute accumulated heat, lowering the overall temperature of the pond. These also aid in the removal of excess nutrients, which can reduce oxygen levels as they fuel algal blooms.

6) Consider covering the pond during the hottest time of the day

Summer tilapia pond with shade cover
Installing a pond cover may be necessary in regions found closer to the equator, where temperatures are more extreme. Ursus sapien, CC BY-SA 3.0, via Wikimedia Commons

In regions found closer to the equator, both the light and temperature intensity can peak to truly dangerous levels at the height of summer. It may make more sense to install a retractable, awning-like contraption or to manually place some form of pond cover over the water’s surface. This should block direct sunlight and reduce overall heat absorption. Come late afternoon, you may remove or roll back the pond cover.

If you’re working with a budget, a shade cloth, tight mesh/net, or a recycled frame should work! To maintain the appearance of a more stately pond in a well-manicured garden, you might consider placing a temporary pergola or a shade sail over some sections of the pond. Simply make sure that the material you use does not deteriorate under the heat and inadvertently pollute the water’s surface.

7) Consider using an aquatic dye

Applying aquatic dye to pond
Applying aquatic dye to your pond can help control algae growth and keep the water cool. USFWS Mountain-Prairie, CC BY 2.0, via Wikimedia Commons

Non-toxic pond dyes, which are usually blue, black, or a mix of these two tones, are frequently marketed as a means to control algal growth. Made with pigments that are similar to those found in food-safe dyes, these are often added to public water features to minimize light penetration. The reduced light prevents increases in photosynthesis rates, thereby controlling the growth of excess algae. As the amount of solar energy absorbed by dyed water is reduced, the water temperature can also be maintained.

Using aquatic dye is especially beneficial for ornamental and recreational ponds where maintaining clear water and a stable ecosystem is essential. For example, in a garden pond with koi fish, adding dye can help keep the water cooler, creating a more comfortable environment for the fish while also enhancing the pond’s appearance with a rich, uniform color.

8) Boost your pond’s water circulation rates

Ornamental water fountain
Any water feature that can generate splashes and fine droplets is useful when you wish to keep your pond cool. Gouwenaar, CC0, via Wikimedia Commons

Have you ever noticed how rapidly-flowing rivers and streams have consistently cool water, even at the height of summer? When water is in motion, the surface area exposed to the air is increased. This is why fountains and waterfalls are fantastic instruments for rapid heat exchange. The movement also mixes warmer surface waters with cooler water from deeper layers, maintaining a more consistent overall temperature.

By leveraging these physical principles, you’ll find that some of the most aesthetically pleasing and functional water features can be designed to keep a pond cool on the hottest of summer days. Pond spitters, minimalist fountains, and multi-level waterfalls can work hand in hand to generate splashes and fine droplets, forcing heat to escape. As a bonus, these features also boost the effects of a pond pump as they improve oxygenation rates!

9) Get creative

Old bedsheet
Even with a low budget, you can keep your pond cool! For example, an old bedsheet can be repurposed into a shade cloth. Pink Sherbet Photography from USA, CC BY 2.0, via Wikimedia Commons

Given the tips enumerated above, you’ll find that keeping a pond cool involves a blend of innovative solutions and attentive care. It seldom has to be complicated, however. Combine a few strategies and welcome any ideas that encourage recycling or re-using waste or tools in the home. You can string up empty water bottles to create a suspended mosaic that reflects light. Even an old bedsheet, left unused at the bottom of a shelf, can be given renewed purpose as a makeshift shade cloth. With just a touch of ingenuity, you can safeguard your pond against intense summer heat!

Angeline L
About the author

Angeline L

I'm a passionate researcher and scuba diver with a keen interest in garden plants, marine life, and freshwater ecology. I think there’s nothing better than a day spent writing in nature. I have an academic and professional background in sustainable aquaculture, so I advocate for the responsible production of commercial fish, macroinvertebrates, and aquatic plants.

Read more about Pond Informer.

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