I've got a rather large pond in my garden and I'd like to reduce it's length by about 10m. The intention is to build a barrier across it, fill in the reclaimed bit in and lawn it. Question is what to use to build the barrier ? I don't want to spend a fortune and if I can't do it economically I'll leave it alone. One of the problems is the depth. The water is about 1m deep but there's an awful lot of sludge at the bottom and if I used gabions (for example) I won't know where they'll settle until it's too late. They'd also probably be too expensive.

I could just start filling it in from one end and stop when I get far enough but then the water would soak into the new area. I don't think the pond has a liner and it's been there for at least thirty years. Draining the pond is not an option.

There's plenty on the internet about building a pond but nothing about shrinking one ! Any ideas ?