Normally liners only stay supple for a short time but I would see how bendy it still is. Ideally you would have wanted to them to build it neatly in the first place but shallow shelves in the margins can sometime be manipulated with some well placed rocks or a little digging under the liner (just lift the liner gently and excavate the soil so the pond sits more level). Putting some flat rocks on top of the folds can press them down and create different water depths behind it but it does depend on how much give there still is in the liner because it can become very stiff in time. I used to work in aquatics and you wouldn't believe how common the problem is. If you are happy to have the pond there then it can be tidied up with rockwork which can also make it more inviting to wildlife, so have a little play with the edges and a think before you decide if it needs to be completely removed.
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I used to work in aquatics and you wouldn't believe how common the problem is. If you are happy to have the pond there then it can be tidied up with rockwork which can also make it more inviting to wildlife, so have a little play with the edges and a think before you decide if it needs to be completely removed.