Do you have fish in there? If not, you can spray the plants with Round-up herbicide to kill them. They will be easier to remove if they die back. Then you can just start over. Monsanto (the makers of round-up) claim you can use Round-up in the presence of fish, if you follow their directions. They are, of course, talking about natural pond, so I am not sure how well it would work in a liner pond.

Here is a link that might be useful: round-up for aquatic weed control

I don't use anything around my ponds ever since I found out (from a previous thread) that frogs and toads breathe through their skin. Even roundup can be toxic to them. Thus my yard and pond has been taken over by the weeds. I kind of like the natural look and the frogs and toads love too hide in them. It has just been to hot to hand weed (90º+ with sweltering humidity) so the weeds have had their freedom in my yard this summer.

Jenny

Hi Charle 7 - I, have a gardening friend and we help each other out in the garden. So, here is what we did with her pond to clean it up. We drained it first, to be able to see the plant roots as it was a jungle of tangled masses- just as you mentioned.
As we drained it down, then we could see all the growth.
We had to get in the pond and pull the heavy plants up and we used large knives to cut the plants apart. That was the only way to get at the plants, they were sooooo heavy with all the roots!!!!!
It took us three hours, to get her pond in great shape.
If you can, ask a friend or two for help.
You will need it, as plants grow and multiply so fast in a pond. If , you get to clean out your pond - I would love some of the plants. Let me know ,if you would like to trade!
Good luck, tina

Hi Charle, Wish you luck in the entire cleaning process!
Since we are in the topic of ponds, I'd recommend getting a pond filter or some sort of uv clarifier if u are going to put fish there. It really helps the maintenance aspect of owning a pond and the good thing is that you don't need to keep buying filters because some models allow you to just clean the sponge part of the filter.

Absolutely do not use round up, even if the makers say its possible to use around fish. Round up had been a proven cause of cancer in humans and should be avoided. Introducing it to your pond can poison your fish and wild life that come visit.