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Need help finding a leak in liner pond.

Posted by larryl 7 Southern Oregon (My Page) on
Sun, Nov 29, 09 at 15:25

I have a 30-50 gallon a day leak. The leak has been there for a couple of years, and I am getting tired of adding water all year long, even in the rainy season.

I have seen no sign of wet earth around the pond perimeter.

My system is three ponds that share circulation. I shut off the pump and let the system stop all circulation. Two of the ponds showed no loss of water even after three weeks, so I know the leak is in the third pond. The third pond dropped about a foot and then stopped dropping, so I know the leak is somewhere on the current waterline. I also know the leak isn't in the waterfall or other connecting passages.

Here is the problem. I have looked all around the perimeter and can't find the leak. There don't appear to be any obvious holes. If anyone has any tips for what to look for, or how to find the leak, I would like all the help I can get.

The liner is about ten years old. The pond in question has always been kept full so the leaking area has always been under a foot of water until now. The area of the exposed waterline is mostly pretty vertical. The pond is dug into decomposed granite which produces a fairly smooth hole. I have had a few moles digging around the pond over the years. I get a little ice around the edge in winter, but it never covers the whole pond. I do occasionally have deer fall into the pond. I have had a couple of perimeter rocks become dislodged and end up on the bottom.

It is a fairly large pond with some hefty koi, so replacing the liner is something I would like to avoid if I can. Catching the fish and replacing the liner would be a major task.

OK. What should I be looking for? And how do I find it?

Follow-Up Postings:

RE: Need help finding a leak in liner pond.

  • Posted by horton 6 b Ontario. (My Page) on
    Tue, Dec 1, 09 at 8:37

Larry, do you think that one of the deer has caused a small puncture with its hoof, as it fell into the pond?
Or one of the moles has caused a small tear in the liner?

There is a continuous leak in my ponds also that I cannot locate. If left alone, with no top-ups, the ponds lose about six inches of water over a three week period. Combined, they have a surface area of approximately 12' X 15'. The level stays at that lower point thereafter.

I have searched and searched, time and time again to locate the culprit, without any luck. I'm not as yet ready to go stripping all the stone work out from around the perimeter to find this small but annoying leak.

I use a timer set up to top up the pond early in the morning, so on a day to day basis I don't see the water loss.
It is only in the winter when I have shut everything down that the true effect is seen.

Sorry that I could not be more helpful, I do feel your frustration, it can be such an annoying elusive thing, plus the cost of the water top-ups.

In the summer with the "what you don't see........" attitude I guess I kid myself into believing that everything is fine.
Good luck with your quest to find the leak and when you do find it, please post an update. Maybe that will motivate me into doing something more about my situation. LOL

RE: Need help finding a leak in liner pond.

Larry - several posts over the years recommend pouring milk in the pond to locate a leak--theoretically the milk will swirl and you will see a flow toward the leak. Try it after the water has gone down to the leak level. I suppose you would need fairly still water for this.

Here's hoping the leak is in an easy location to fix.

RE: Need help finding a leak in liner pond.

Leaks can be sneaky to locate. A shallow shelf can be a place where some clawed animal stomped holes where sediment collects and masks it, it could be a cats claw slash going into the fold of a liner, a turtle that sheltered in the cover of overhanging plants, a sharp root that the liner settled on... A rodent pecking for water during Winter freezes, a storm tossed branched that lanced the liner and snapped off on impact.

The leak on the third pond helps that it is known to be at about one foot depth, you stand a chance of draining the pond and getting a patch on it without too much disruption.

If you shake say, a half cup of koi clay onto a couple of cups of water, going round the pond when the water is very still and dropping clouds of clay water in, the clouds of water might be drawn to where the leak is and indicate its location. That quantity of clay will be benign in the water.

Otherwise you are rather stuck with letting the water level drop to the level of the leak and keep plugging away at doing fingertip searches

RE: Need help finding a leak in liner pond.

  • Posted by larryl 7 Southern Oregon (My Page) on
    Tue, Dec 1, 09 at 15:32

I included the information about deer, moles, and ice because they are certainly possible causes, but I have no reason to believe any one of these actually caused the damage. As for deer, I suppose the most likely scenario would be a deer trying to get out of the pond and trying to get a purchase on the bottom with its pointy little hooves. When they fall in they usually go in head first with little flailing. I put in a deer escape point when I dug built the pond. It consists of a slightly sloping shelf at a depth of two feet with some rocks on the shelf. The leak appears to be higher than the deer shelf, so I kind of doubt it happened that way.

As for moles, I have seen a number of their tunnels near the pond and have always wondered if they posed a risk to the liner. Other than that I don't have any other reason to suspect mole damage.

I assume the liner should last longer than a decade. In any case I would expect the liner to fail first where it was exposed to the most sunlight, not under a foot of water. So, I'm ruling out normal aging of the liner.

Mike, I think the milk test might work if the pond was leaking at a higher rate, but I'm only losing 1-2 gallons an hour. I have a hard time imagining that even a carefully applied dribble of milk would move toward a small hole at a rate that could be observed before the milk dissipated. I might give it a try just to see what happens on the theory that it can't hurt to try it. If anyone has actually tried this before let me know.

sdavis, since the leak is in a vertical part of the pond wall I don't think it is covered by sediment. The folds do give me some concerns. There are numerous folds in the vertical sides that are really hard to inspect. I can feel into the folds, but I can't see into them very well. Right now the water is very cold, so I can only probe for leaks for so long before my fingers get numb. I'm hoping to refine my search technique to look in the most likely place. And it would help to know what to look for.

Thanks to all for the help. I'm still open to ideas if anyone has anything else.

RE: Need help finding a leak in liner pond.

Larry--I can't swear by the milk technique, but a search showed up several ponders suggesting it--pour around the edges, maybe short distances at a time. At one time it was the conventional wisdom here.

I have used cornmeal successfully twice to plug up small leaks. I think it gets drawn into a small hole, swells and possibly binds with fine soil particles under the liner. The leaks stopped for over a year. I posted this previously and the reaction was non-believing, sort of voodoo pond tending. Although one respondent noted that cornmeal was used to stop leaks in navy ship boilers during WWII. Same deal, sprinkle around the edges. Another one of those "what can it hurt for a couple of bucks?"

My guess is that losing 1-2 gallons per hour is too much for the cornmeal but should be enough to make the milk work.


RE: Need help finding a leak in liner pond.

  • Posted by horton 6 b Ontario. (My Page) on
    Tue, Dec 1, 09 at 17:10

Yes Larry it was the deer getting out of the pond part that I thought could have been when a small incision was made by a flaying hoof.

I have used slowly poured milk to find leaks and it can work.
I had a couple of leaks after installing the liner. They were due to folds in the liner acting as siphon tubes after a heavy rain had filled the pond to the brim.

Even after the level had returned to normal by draining out at a low spot,the water had kept going down over for few days.
This happened a few times until I decided to try the milk tracing trick.
I poured milk around the perimeter here and there and soon saw it coming out at a low spot onto the ground where a couple of folds in the liner came over.
I just pumped some silicone seal into the folds to plug them up and that cured that particular problem.
Hope this helps.

RE: Need help finding a leak in liner pond.

I have found and fixed more pond leaks than I can count. In this case I would lower the water level to about six inches below the leak. Get in the water and go slowly around the edge with a sponge and wash-cloth, sort of rubbing and drying and looking, up close.
Even if it's a pin-hole you will see it. Moisture comes through from the backside as you wipe/dry.

RE: Need help finding a leak in liner pond.

  • Posted by larryl 7 Southern Oregon (My Page) on
    Thu, Dec 3, 09 at 0:18

Thanks Bubba. I think this is the plan for me, except for that getting into the water thing. My water temp is right at 32 degrees on the surface right now. I'll give it try with my head hanging over the edge and try not to fall in head first like the deer.

Based on the leaks that you have found and fixed, what do you think is the most likely cause of a leak in a pond that started to leak after a decade of not leaking?

RE: Need help finding a leak in liner pond.

A plank across the pond can make it easier to search awkward places, saving a dunk in the water

ahah, remembered a few more techniques for finding leaks... Let the water level drop below the leak, wait for a very dry period of weather, go look by day and by night for little tiny beads of moisture showing up on dry areas of the liner where soil moisture is moving through small punctures.

You can spot pinhole leaks easier when the liner is very dry while the soil behind is quite damp.

During Summer, its not unusual to see tiny trails of debris trickling from punctures on a dry liner, ants find every tiny hole convenient for tipping out little particles of excavated soil as they extend their tunneling.

Rodents can be an occasional source of leaks, where in hard winters they cannot find water in frozen ground, they tunnel up to the liner and peck through the liner usually in out of sight places, beneath overhanging clumps of grass, folds in the liner... As their holes cause the water levels to drop, they bite new holes at another location lowering the water level further.

Where you can look behind the liner will indicate if their are rodents, you might anticipate several leaks along where those tunnels run after a hard freezing Winter. Moles do the tunneling, mice move in and bite at liners

RE: Need help finding a leak in liner pond.


sdavis, above is correct about the rodents. Also, a spot under the liner with no padding. One little pebble over time will do it. Dog claws, deer hooves, falling branches, etc. Sometimes you never know.

One of the more interesting ones was a bear. He got in a pond that was about the size, for him, of a giant bathtub. Proceeded to try and catch goldfish. There were giant claw marks everywhere. Replaced the liner.

Know anyone with fishing waders?

Also. There is this stuff called 'Rescue 911' that comes in a spray can. You can spray a few coats over a pin-hole type leak.


RE: Need help finding a leak in liner pond.

I have a similar issue with my pond- will folds in the liner cause this issue of "wicking"? If so, I could just look under the liner fold and see if it is wet from wicking- can't imagine the water wicking that fast though

RE: Need help finding a leak in liner pond.

I have been playing with liner ponds for the last 20 years and the last 13 years it has been my full time job. I have found and repaired hundreds of leaks in ponds and waterfalls. I have heard about wicking of water by the liner for all 20 years. I have never seen it happen. One winter during my slow time I spent over 40 hours trying to get water to wick up a liner. I tried everything I could think of to get it to wick. I ran over 70 experiments and I could never get the liner by itself to lift water even a 64th of an inch. I do not know if it is possible for liner to wick water but I doubt it. Yes it is possible to get liner to siphon water out but the siphon has to be started and this is not wicking. And it was extremely difficult to get it to even siphon with just liner. In order for a pond to loose one gallon per day it takes a hole loosing one drop per second. So depending on how much water a day that you are loosing will determine how big a hole you have to find.

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