A water feature’s ambient temperature regulates when maintenance is performed, when equipment, plant or animals care is needed, and the dangers of too cold or too hot of water poses to all living things.  Remember, the total system volume and depth of the water feature can help maintain steady temps. Further, ensure to have a floating thermometer in you pond system at all times.  NOTE: The optimum temp should match the care instructions of flora and fauna as well as align closely to your climate.

Freezing Water: When your system’s water is less than 35°F, this is freezing cold.  Most plants and animals will die (although there are some amphibians and insects that can freeze solid and later thaw out unharmed).  A person or animal submerged in water this cold can die within 15 minutes of hypothermia.  A frozen over pond may fool a person or animal that it’s safe to walk on as well.  Always maintain a safe pond perimeter. Depending on the volume of the pond, the subsurface may not freeze, but the pond forms a cap of ice.  Again, the flora and fauna may be okay beneath, but over time, oxygen levels will drop and toxic gas accumulates.  Add a breather (a heated aerator) to keep O2 levels up without dropping the water temp further.  A pond ice preventer will keep the surface from completely freezing allowing for out-gassing too.

Extremely Cold Water: When your system’s water is 35°F to 45°F, this is extremely cold.  Ponds should be in “winter mode” and you should not feed fish at this time.  Many cold water fish, plants and animals can tolerate this, but may die if they are subjected to freezing.  In climes where long, cold winters exist, a pond heater may be appropriate to keep the water from dropping further.  Beware that extremely cold water can be deadly within 15-30 minutes from hypothermia for people and animals that fall into it. 

Cold Water: When your system’s water is between 45°F and 55°F, this is cold water.  When water temp warms up and consistently reaches 50°F to 55°F, in the spring, this is the time to begin pond start-up.  Conversely, when the water cools down and consistently reaches 50°F to 45°F, in the fall, this is the time to begin winterizing your pond.  Beware that temperate water plants and animals may only be able to tolerate this range, but no colder.  Cold water presents a real hypothermia danger within 30-60 minutes.  If working in such conditions, wear a dry suit or heated gear as this temperature is unsafe for even short periods of time.

Extremely Cool Water: When your system’s water is between 55°F and 65°F, this is extremely cool water.  For sub-tropical plants and animals, this may be the lowest temps they can endure for short periods.  When the water is consistently 60°F or above, summer food, water treatments and such should be employed.  Remember though, even these temps can cause hypothermia (but may take 1-2 hours before occurring).  Wear protective gear if working for extended periods in such conditions (like a wet suit).

Cool Water: When your system’s water is between 65°F and 75°F, this is cool water AND is the optimum cold water fish and bacteria water temp.  For tropical plants and animals, this may be the lowest temps they can endure for short periods.  Long periods of immersion in cool water can cause hypothermia (2-12 hours).  Be sure to keep dry or wear layers when submerged in the pond.

Neutral Water: When your system’s water is 75°F to 85°F, this is optimum temps for most types of fish and plants.  Fish gain the most growth during this time, and plants will flourish due both to sunlight hours and warmth.  This is a great time to add new fish or plants too.  Oxygen levels are still maintainable.  Note: Any warmer and a decline in the amount of dissolved oxygen level begins.

Warm Water: When your system’s water is 85°F to 95°F, this is warm water.  However, over 85°F, the water begins to lose its ability to hold onto oxygen (less than 7.6ppm at max saturation).  At the high end, fish become hyper, eat more (and create more waste) and deplete oxygen at a faster rate.  To lower the temps, make temporary shades from any direct sun from hitting the water if possible, use pond dye, aerate more, perform 10% water changes at night (if the potable water is cooler), and cut back on feeding the fish so they produce less waste and eat additional algae.  Add water treatments at dawn (not mid-day).

Extremely Warm Water: When your system’s water is 95°F to 105°F is extremely warm.  Even without fish, at 95°F, bacteria begin to die leading to ammonia spikes due to plummeting bacteria that are starving for O2.  The entire nitrogen cycle will begin to break down.  If all the above stopgaps used in warm water do not help, consider water chillers that can be added to your system (either permanently or temporarily).  Ensure to drop the water temps slowly (1°F per hour).  Do not shock your system (for example: don’t throw ice in the pond for instance) as this would be disastrous for pond life.

Hot Water: When your system’s water is more than 105°F, this is hot water.  There will be little or no oxygen, fish and plants will readily die in this water, and the entire nitrogen cycle will fail.  In other words, it’s a sterile environment for all the beneficial pond life you want.  However there is undesirable pond life that can thrive in such conditions such as insects, protozoa, fungi, and non-beneficial bacteria!

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