A METHOD OF OPERATING A CLOSED PHOTOBIOREACTOR (1) FOR CULTIVATION OF PHOTOTROPHIC MICROORGANISMS.THE PHOTOBIOREACTOR (1) COMPRISES A CULTURE LIQUID AND IS PARTIALLY OR COMPLETELY SURROUNDED BY WATER OF A WATER BODY (2). A DENSITY DIFFERENCE BETWEEN THE CULTURE LIQUID AND THE SURROUNDING WATER IS PROVIDED SO THAT THE POSITION OF THE PHOTOBIOREACTOR (1) IN THE WATER BODY (2)IS CONTROLLED.A CLOSED PHOTOBIOREACTOR (1) FOR CULTIVATION OF PHOTOTROPHIC MICROORGANISMS. THE PHOTOBIOREACTOR (1) IS ADAPTED TO COMPRISE A CULTURE LIQUID AND TO BE PARTIALLY OR COMPLETELY SURROUNDED BY WATER OF A WATER BODY (2). THE PHOTOBIOREACTOR (1) COMPRISES MEANS FOR DETERMINING THE DENSITY DIFFERENCE BETWEEN THE CULTURE LIQUID AND THE SURROUNDING WATER.
