Abstract: Methods for increasing the levels of lipids in oleaginous algae are described. Lipid levels in algae can be increased by stress, such as nutrient stress, after which the lipid can be harvested from the algae using a non-destructive extraction process. The stress may be provided in a periodic or “pulsed” fashion. Lipid levels in oleaginous algae can also be increased using simulated stress by treating the algae with a chemical inhibitor or by using recombinant technology to insert a sequence expressing a protein such as a nitrate reductase inhibitor that is expressed when a stressed state is desired. A method for maintaining the temperature and water levels of algae ponds using buoyant spheres is also described.