Hello fellow pond enthusiasts,

I'm in the process of constructing a pond and would love to get some advice from those with experience in concrete pond construction. The pond has been excavated, revealing a sloping bedrock at the bottom. The sides are steep, almost vertical, and part of the pond structure is above ground, reinforced externally with a thick layer of soil and stone.

I plan to use concrete blocks for the sides, but I want to maintain the natural slope of the bedrock. To do this, I'll need to create a level base or foundation around the sides on the bedrock before setting the blocks. What would be the best approach for building the foundation? Could a circular slab reinforced with rebar work? What would be the best waterproofing agent or coating to apply to the concrete to prevent water leakage and protect aquatic life from the alkali content of the cement?

I'm aiming for a durable and eco-friendly solution that ensures the health of the pond's ecosystem. Any tips, product recommendations, or construction techniques would be greatly appreciated. I know that it would be easier to just use a pond liner but I am optíng not to.

Maybe @DoghouseRiley would know.

My suggestion would be to reconsider the pond liner. I have two friends who tried small concrete ponds but both developed leaks after a few years. They were told that they probably didn't have a proper layer of sand underneath to support the concrete uniformly. Most waterproofing will affect fish.

In a previous house I recycled a large fiberglass form used as a fish box in a boat. I put a reinforcing coat of fiberglass on the outside so it wouldn't affect the fish.

I now have a 3x5 pond made from heavy liner which is still going strong after 5 years with plants, fish, and bull frogs. There are in balance and I don't feed the fish. I have a small solar pump to keep the water moving.

Someone on here may have practical suggestions for a concrete pool. Obviously concrete swimming pools are sturdy but I have found that the liner is much easier and is durable. By digging the hole you have done the hard part.

Good luck with your progress.

Thanks for the reply. I could drill into the bedrock. The problem is that it is on a rather steep slope, where at the shallow end it is only about 50 cm (20 inches) deep and at the deepest end it is almost 200 cm (80 inches). The bedrock is a great seal, it doesn't leak any water from there. The problem is the sides that consist of very porous soil. This is one of the reasons why I would prefer not to use a pond liner, it simply wouldn't be necessary for the bottom of the pond. I want to find a method to seal the sides without covering the bedrock.

I have seen some videos where they use shotcrete. I don't know much about it, but it looks like it could be a possible solution.