After thre years, I have finally cleaned the bottom of our pond.
The water is very clean. There is just this layer of grime that seems
to build up. Seems like the internal flow deposits it along one side.
It gets stirred every couple days as I scoop out leaves.

Anyway, I borrowed a 5.5 hp 16 gallon shopvac. I was amazed, no shocked
at how fast it sucked up 16 gallons. Sucked out nearly 40 gallons to clean
out
a 1200 gollon pond. Our pond is conc. I can't imagine using this with a
liner.