Collect organisms to grow larger and stronger. Collect red colored organisms to go to a lower depth and blue to go up near surface. http://1game.free.fr/online-flash-games/Flow.php
I saw a video of this yesterday. Finally beat the blue stage and am in the yellow. Blue stage was a bit boring because it needed more organisms around. Yellow stage is a challenge, not easy at all. It's easier for me to move around with the organism in the blue stage than the one in the yellow.