Cedar will also release oils and tannins.
It looks really awesome, but turns the water.
Just to test it, I tried a piece that had been submerged in a freshwater creek/mini river for many years.
My father in-law remembers seeing it there more than ten years agoAt that time it was 90% totally submerged all the time.
When I got it out the creek bed had eroded to 4 ft below the piece that had become trapped in the bank (4ft high)
So it had been submerged for years and then sun baked for years.
It STILL released oils and tannin into my test tank.