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How shallow of a pond/pool can fish survive in?

 
master gardener
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I'm hoping to dig a few small pools over the next few months, that will most likely be just a few feet wide and deep, and I would like to have some with fish, and some without fish.

These will be just filled with rain water.

I've been reading about the depth needed for fish to survive the heat of summer and the cool of winter, and am seeing a wide range of depths mentioned, so I thought the best thing may be to ask people here what they've actually seen.

I'm guessing the range may be due to the size of the fish, with smaller fish being able to survive in more shallow water, and bigger fish needing deeper water.

What's the shallowest you've seen fish survive and what kind were they (if you know) ?
 
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We had Bluegill in our seasonal creek at about 18 inch depth of water.  My aquaponics tanks are maybe that deep, with Bluegill doing very well.

Really tough fish like Bluegill can live in shallow water, but something like Bass or Trout might require deeper water which can stay cool in hot weather.

In both the above situations, the water was moving, so there was good aeration.  Still or stagnant shallow water will kill fish right quick.

 
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One consideration is predators - too shallow, and a heron or raccoon can clean you out pretty quickly.
 
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It will depend on your weather, In my climate the only consideration is that it must be deep enough to not freeze solid in winter so about 3ft is fine here. That also gives enough depth to hide from herons and cats.
 
Steve Thorn
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I wonder if I could plant lots of water plants to help clean and oxygenate the water, and the fish could also hide from predators in the plants.

I also have some rocks that I plan to put in the bottom and along the side to help regulate the water temperature and provide more shelter and habitat.
 
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If it is spring fed/flowing then 1ft in the summer and less than 2ft in the winter.
If it is a pond/stagnant then 3ft to prevent overheating in the the summer and whatever the frost depth in the winter +1ft.

So the short answer is 3ft.
 
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I think it's also highly dependent upon the species.  Largemouth bass and bluegills are a farm pond staple around here.  They can handle a bit warmer water and less oxygen (I think).  Trout are trickier.  Some species are probably even easier (catfish? carp? bullheads?) in mucky low oxygen waters.
 
Steve Thorn
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I'm interested to see if I can get them to hold water year round. I have a few really wet places that I think could hold the water well.

I guess I could see which ones hold water for the year and then add fish to those after that. It would probably give some time for the plants to get established also.
 
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    Really great information here. I need it for the pond I’ll be digging in the spring. I wasn’t sure if I was planning deep enough.
 
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I think it is very much related to your climate.  In this area, pond depth for fish ponds is at least 10 feet for warm water ponds, deeper for cold water species.

UW-Madison says minimum of 12 feet to avoid winterkill and for correct oxygen levels in summer.

Wisconsin Lake and Pond Resource: "These ponds vary in depth but ideally should be deeper than 12′ and up to 30′ deep at times."

From Michigan DNR: "Minimum depth for sustaining warm water species like bass and panfish is 10 feet. For trout and other cold water species, the minimum is 12 feet or more unless a cold spring or stream feeds the pond. The entire pond need not be this deep, but unless 25 to 50 percent of its surface area lies at such depths, the pond will not provide the right amount of dissolved oxygen in winter and range of temperatures in summer that fish need to survive."

 
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You need to make sure there is air/ water circulation .. we have a 5 metre dam that is dying as it is too deep due to lack of movement .. so we are having to spend $10k on three air pumps.  The fish can not survive this this environment.
 
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Amend should read : 5 metres DEEP!
 
Steve Thorn
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I'm thinking that the minimum depth needed could also vary depending on a few factors.

Shade- Maybe having lots of shade during our hot summers will help cool the water and regulate the temperature during this hotter part of the year. Our winters rarely get below freezing for long.

Lots of water plants- to create highly oxygenated water and additional shade to cool the water and create cover for the fish to hide.

Size of the fish- I'm guessing that really small fish could thrive in really small amounts of water here. I bet most of the sources talking about minimum water depth are referring to raising large sport fish. There are some wild fish here that don't get more than a few inches long at most. These types of fish might be a good fit for small pools.
 
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Some good responses.

It depends a lot on the species of fish and their response to temperature and dissolved oxygen.  

Dissolved oxygen concentrations are (generally) higher in cold water than warm water.  Species like trout have a high demand for dissolved oxygen, and are typically found in low water temperatures (55-70 degrees F they're considered "coldwater" species).  "Cool water" species like northern pike, yellow perch, and walleye like water temperatures can live in temperatures a little higher, but prefer maybe 65-75 degrees.  "Warmwater" species like your typical largemouth bass, channel catfish, and bluegill, can thrive in temperatures upwards of 75 degrees. Some species are specially adapted- gar and bowfin can gulp air from the surface, topminnows and killifish cruise just under the water surface, where oxygen concentration is high.  So short answer: depending on what species you're interested in, minimum depth can be a couple inches or dozens of feet.  

Small ponds warm up faster (and get warmer) than small ponds, shallow ponds tend to have more oxygen than small ones (greater interaction with the atmosphere).  Shallow ponds also tend to have more aquatic vegetation, which may or may not be a good thing depending on your management goals.  

If you're in an ice-free (or largely ice-free) area, 4-5 feet is probably adequate for most fish species.  If you get ice cover for more than a couple weeks a year, you may consider depths closer to 8-10 feet.  If you're willing to run a pump during winter to keep open, ice-free areas, you could probably get away with a shallower pool.  

I'm a big proponent of small, fishless pools.  Lots of invertebrate and amphibian species have been declining over the past several decades due to landscape alteration and chemical spraying; thanks for incorporating some into your plan!
 
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Steve Thorn wrote:I'm thinking that the minimum depth needed could also vary depending on a few factors.

Shade- Maybe having lots of shade during our hot summers will help cool the water and regulate the temperature during this hotter part of the year. Our winters rarely get below freezing for long.

Lots of water plants- to create highly oxygenated water and additional shade to cool the water and create cover for the fish to hide.

Size of the fish- I'm guessing that really small fish could thrive in really small amounts of water here. I bet most of the sources talking about minimum water depth are referring to raising large sport fish. There are some wild fish here that don't get more than a few inches long at most. These types of fish might be a good fit for small pools.

plants will oxygenate while alive but when decomposing will rob O2. id get a backhoe in there and dig as deep as they can. a small deep pond is better than a large shallow one esp. in your climate. plant a lot of fast growing water loving shade trees around it will help keep water temps down. around here people look for natural springs to build their ponds near which will give some cool water in the heat of the summer. you don't need much water flow to make a big difference. good luck!
 
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