Depending on your bank and slope where you are going to put them, might be able to "roll" them down by hand (staying on the up side of course) to the bottom or a ledge or post driven into the pond bottom. Roll by hand several down into a cluster.
Then if they are not so heavy so you can lift one end, end it up on top and move it down the ling. If you can lift one end, might be that two stout guys could manipulate them in the water as long as they were not too deep to stand on the bottom.
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