A fish hatchery wants to determine how many fish can survive in its artificial ponds. To instill the water with O 2 necessary to support life, pumps are installed at the centers of the rectangular ponds. The pumps bring water to the surface and the water travels outward in contact with the air. When the water reaches the edges it is pulled downward and eventually reaches the pumps. The outdoor breeze is sufficient to ensure that there is no resistance to mass transfer in the air