NOVELTY - Harvesting a non-vascular photosynthetic organism (NVPO) from an aqueous culture comprises: either mixing a polymer flocculant with the aqueous culture to form floes of the NVPO, introducing dissolved air into the mixed aqueous culture, and collecting the floes of the NVPO, where the aqueous culture has a total dissolved solids (TDS) of at least 1500 mg/l; or mixing the polymer flocculant and/or a coagulant with the aqueous culture of the NVPO, where the flocculant and/or the coagulant interact with the NVPO to cause sedimentation, and collecting the sedimented NVPO.    USE - The method is useful for harvesting a NVPO from an aqueous culture in an open pond including a natural pond and an artificial pond, where the NVPO is unicellular and multicellular (all claimed), and the NVPO includes microalgae for producing oxygen by photosynthesis, for biotechnology applications for many reasons including high growth rate and tolerance to varying environmental conditions, in a variety of industrial processes for commercially important products, for producing nutritional supplements, pharmaceuticals, natural dyes, a food source for fish and crustaceans and biological control of agricultural pests, for removing nitrogen, phosphorus and toxic substances in sewage treatment, and for controlling pollution such as biodegradation of plastics or uptake of carbon dioxide.    ADVANTAGE - The method is capable of efficiently harvesting the NVPO from the aqueous culture without the aid of air floatation.    DETAILED DESCRIPTION - Harvesting a non-vascular photosynthetic organism (NVPO) from an aqueous culture comprises: either mixing a polymer flocculant with the aqueous culture to form floes of the NVPO, introducing dissolved air into the mixed aqueous culture, and collecting the floes of the NVPO, where the aqueous culture has a total dissolved solids (TDS) of at least 1500 mg/l; or mixing the polymer flocculant and/or a coagulant with the aqueous culture of the NVPO, where the flocculant and/or the coagulant interact with the NVPO to cause sedimentation or increase the sedimentation rate of the NVPO, and collecting the sedimented NVPO. INDEPENDENT CLAIMS are included for:    (1) an aqueous culture comprising the NVPO at a concentration of 0.001-0.2%, and the polymer flocculant at a concentration of less than 10 ppm;    (2) a biomass slurry comprising the NVPO at a concentration of at least 0.2% and the polymer flocculant, where the ratio between the weight of the polymer flocculant and an ash-free dry weight (AFDW) of the NVPO is at most 1.5%; and    (3) an aqueous medium comprising the NVPO at a concentration of 0.0001-0.02%, and the polymer flocculant at a concentration of less than 1 ppm.