In an embodiment of the invention, aqueous growth medium in a pond can be used to grow algae which can be pumped to a primary dewatering device where the algae can be separated from the harvested growth media based on the flow of the harvested growth media and gravity. The flow through the primary de-watering device can be optimized to maintain log phase growth in the pond, while minimizing the pumping cost and maximizing the concentration of total solids in the primary de-watered algae.