Has anyone at PondBass just tried putting a strip of pond liner in the swimming area to thwart bottom-rooted plants?

You would probably have to start at x? depth (or place a buoy rope) so non-swimmers cannot wade to the slippery liner and slide into water over their head!

I would not use landscape material, because I think the mesh would trap silt and organics from the pond, and plants would start growing on that substrate and then fine roots might be able to reach through to your bottom sediments.

If you started to get sediment accumulations on the liner after several flooding events, maybe you could sweep it clear with a trolling motor, or even your big outboard motor?