During extreme summer heat, pond water holds less oxygen, which can stress koi and other pond fish. Increasing aeration, providing shade, and maintaining good water circulation will help protect your fish.
Watch for signs of heat stress
Use a pond thermometer to monitor water temperature, especially when it approaches or exceeds 80°F (27°C).
Watch for fish:
- Gasping at the water's surface.
- Gathering near waterfalls or streams.
- Becoming unusually sluggish or showing reduced appetite.
If fish are gasping at the surface, increase aeration immediately.
Increase oxygen and circulation
- Keep waterfalls, streams, and pond pumps running.
- Add a pond aerator to increase oxygen availability.
- Make sure water circulates throughout the pond without stagnant areas.
Provide shade
Use waterlilies and other aquatic plants to shade approximately one-third to one-half of the pond's surface. Trees, shrubs, and other overhead shade can also help reduce direct sunlight.
Maintain good water quality
- Feed fish in the morning and avoid overfeeding.
- Remove uneaten fish food.
- Remove dying leaves, flowers, and other decaying debris.
If additional cooling is needed, a small partial water change with cooler, properly conditioned water may help. Avoid sudden temperature changes that can shock fish. Treat tap water with a pond water conditioner before adding it to the pond.