Methods for increasing the growth and biomass of algae and algae lipids by growing the algae in the presence of a polycationic substance such as soluble or insoluble chitosan and/or chitin are disclosed. Also disclosed are methods of harvesting algae from an aqueous environment by growing the algae in aggregated clumps and/or mats (formed by the inclusion of soluble or insoluble chitosan and/or chitin or other polycationic or cationic substances) that can be easily removed from the aqueous environment either by filtration, surface skimming, and/or growing in a porous containment device, such as a natural or synthetic fabric, and removing the fabric from the aqueous environment containing the aggregated algae. The methods disclosed have direct applications in biofuel and energy production, agricultural feedstock production, nutrient production, greenhouse gas reduction, removal of microconstituents from water, and water reclamation.
