The pond we took on was made of concrete, and water was constantly leaking from it. When carrying out the project, we initially planned to redo everything: from the base of the stream to the pond bowl, since it is a single system. But the client persuaded us to make only the pond, the stream, he assured us, has good waterproofing, and there are no complaints about it. We agreed and the remodeling began. We hollowed out the concrete, made a frame, laid the waterproofing. And when everything was ready and the pump was turned on, we got this picture.
And so, until we found the reason, the pond was dismantled several times, because the pump (40 cubic meters) was structurally mounted in the film, it turned out that the problem was in the combination of the new and the old. This example once again convinces me that any ecosystem is completely redone. And waterproofing is a separate topic: when the same material is laid by different people, the demand is from the latter. The photo shows the place where the water was leaking under the film.