Platymonas subcordiformis is a marine microalgae that under favorable environmental conditions change metabolism pathways to hydrogen production in direct biophotolysis. Effective hydrogen production by Platymonas subcordiformis depends on application of efficient and economically viable biomass production technologies. In the study, the natural water from Vistula Lagoon was used for microalgae cultivation. No statistically significant differences were found regarding the biomass production in the natural water and synthetic medium. The influence of mixotrophic conditions on growth rate and biomass production of Platymonas subcordiformis was also examined. The highest biogas production of 138.45 +/- 3.39 mL with the rate of 1.15 +/- 0.03 mL/h was noted by the biomass cultivated on synthetic medium with glucose supplementation. Similarly high biogas production was observed by the biomass cultivated on natural water with glucose addition (1.11 +/- 0.14 mL/ h). The use of the waters from Vistula Lagoon resulted in high yields of hydrogen production, which might reduce costs of biofuel production. (C) 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.