When the algae die, they sink to the bottom and decompose in a process that depletes the water of oxygen.
(the algae; die; ) (they; sink; to the bottom and decompose in a process; T:When the algae die) (a process; depletes; the water of oxygen)
the algae they a process
die sink depletes
to the bottom and decompose in a process T:When the algae die
the water of oxygen