How to rid an earthen-bottom pond of elodea ("pond weed")?

We and some of our friends and neighbors have established "pond weed" (elodea, see picture) in our ponds.

This plant had been recommended as an oxygenator, and in some cases it has worked out well. In the case of friends of ours with a series of connected ponds (total volume being at least 18,000 gallons), it's now wildly uncontrolled and taking over their clay-bottom ponds! Despite the weed clogging, our friends still have great water flow-through from a natural spring on their land, and they're afraid that the ponds' outflow water could carry reproductive bits from the weed down as far as the river, not very far below their land.

Any knowledge about how people can eradicate the plant once it's established in earthen-bottom ponds?

Ooh, that seems kind of scary.  I have no idea, but I'll bump this thread.

I don’t know how their pond is set up; but we have a large ( large) pond.  Occasionally we divert the water; let the pond dry and Rake and backhoe the milfoil out.  I compost the milfoil. It looks like a huge amount wet but dries to nothing.

My father did the same thing at the lake we used to own.  He would shut the gate that fed the lake and let the lake level drop and dry out most of the weed.

Neither method is permanent.  But it does clean the problem up for a few years.

See if you can get some grass carp.