Cottonwood is one of the lightest hardwoods around. Less than half as dense as water. I'm going to use a lot of sycamore butts and rootballs in mine, because that's what was there to be cleared, but their specific gravity is not much better than cottonwood, only .56. So, what I did was cut the trunks about 30-40 ft lg still attached to the rootballs. I've stockpiled these outside of the basin until construction is complete. I'll put them back in the pond with the rootballs furthest from shore and about 10 ft of trunk up on the shore. Then I'll stake them to the bank with two stakes each, to keep the trunks perpendicular to shore, until they eventually sink, at which time I'll remove the stakes and trim the trunks down to the shore. Just an idea I had, we'll see how it works.
