I know that goldfish can hibernate but I'd like to keep the water warmer for them. Is moving water colder or warmer than still water? The water shoots out of "pipes" about 3" above the water's surface.

Thank you for your comments, I have disconnected the water pumps that shoots water into the air.

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    $\begingroup$ a fountain will cool down the water and quite fast too,there are some tricks to keep the heat loss down,you can move the pump closer to the surface of your pond this will keep the water undisturbed in the deepest part and you will still have the gas exchange at the surface of your pond.this question fits over at SE.pets too.i have a few decades of experience in over wintering fish in my pond.pets.stackexchange.com $\endgroup$ – trond hansen Dec 26 '18 at 18:48
  • $\begingroup$ I use a fountain (a pump that shoots water into the air and returns it to the pond as opposed to the waterfall itself) to keep my pond a bit less warm in the summer. This takes advantage of latent heat of evaporation and cools the pond water by about 5°F. If you employ such a device in the winter, it would keep the pond a bit cooler. However, if you're referring to the waterfall, friction between the water and waterfall surfaces should keep the water a bit warmer. I don't think I could actually quantify the effect. $\endgroup$ – BillDOe Dec 26 '18 at 20:47
  • $\begingroup$ Do you get a hard freeze in winter? An ice layer will keep the water warmer than the air if the ambient temperature is below 0 C. In that case a fountain can keep the surface from freezing and will cool the water. $\endgroup$ – haresfur Dec 26 '18 at 21:44
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    $\begingroup$ I'm voting to close this question as off-topic because this is not about Earth Science as defined in the help center. However, this would be a great question to ask on Gardening and Landscaping SE. $\endgroup$ – Spencer Dec 26 '18 at 22:45

In nature, fish survive in ponds due to a lack of turnabout of water.

(Fresh) Water has its highest density at 4°C, meaning both warmer and colder water float on top of 4°C water. Wind may push surface water to the bottom, slightly lowering the temperature at the bottom of the pond. Still, once the surface starts to freeze, this proccess is discontinued, creating a temperature-gradient with the relatively warm 4°C water at the bottom - until spring. Thus fish don't freeze to death.

Meaning, leaving your fountain running is a rather bad idea.

As to the issue of possible lack of oxygen - I can't answer that reliably.


In winter the only use of the fountain is decoration ; as commented it will cool the water. As cold water has a higher oxygen content , there is no need for the aeration value of a fountain or moving water. I am sure what goldfish and koi do in the winter is not hibernation, they just slow down. At 50 F they will eat a little . I have tropicals with the koi so I keep the pond as warm as possible , which turns out to be above 50F for my location.

  • $\begingroup$ there is some errors in this answer,koi and goldfish are not able to digest food if the water is below 10C and it is not the lack of oxygen that might kill the fish it is the build up of CO2 so it is a need to keep a hole in the ice to let CO2 out.(winter where i live is below 0C for several months)i do not know where the OP lives. it had been best to migrate this question over to pets beta as this is where the resources to answer this are and it is on topic there. $\endgroup$ – trond hansen Dec 27 '18 at 7:50

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