Ol’ Wally here is having a hard time this year with these assigned letters. So pardon this old squirrel if he, er, cheats a little on O and uses the shape.
Can you readers see that? The pools in this reconstructed stream are O-shaped.
Right, good. But why, you may ask? Our Reston streams had become scoured with run-off from parking lots, so much so that the banks were undercut and soil flowed off with every storm. The lakes were filling with sediments almost faster than they could be dredged. Neither the streams nor the lakes were healthy in this condition, so the humans in charge decided to reconstruct the streams and give their banks new rock armoring.
Two years later, we have trees growing right at the stream edges again and a squirrel can walk right to the edge to get a decent drink.