I have put concrete blocks on several 5 to 6 foot tall Christmas trees for the last couple of years and sunk them in Lake Dardanelle. When I go back to where I put them in the water, they seem to have disappeared after a few days. How much weight- i.e. concrete blocks - does it take to keep a 6 foot tall cedar tree from moving away in normal lake water?? By normal, I mean not out in main current.

I have used aluminum wire to tie the blocks to the trees, so I am sure that it is not a case of the blocks coming loose from the tree.