Heck,
It may be cheaper and easier to dig a new pond and fill the old. Swap the ranges and the pond location or something like that. With the old pond, you have a nice spot to put the diggings from the new pond. Then make sure the banks are set up for easier maintenance. Lead problem? Underground.
Some of us go around our ponds obsessively pulling baby willows and poplar seedlings to prevent this from happening. In my case I need the cattails on one side of the pond for multiple reasons, and the pond level drops too much for easier to control beneficial plants.
