A natural, self-maintaining photoelectric cell, composed of a blue-green algal mat and bacteria as a layered ecosystem, was isolated from a shallow marine bay in Texas near Port Aransas. In daytime the open-circuit potential across the ecological membrane was about 0.43 volt. The efficiency of conversion of light energy to organic potential energy before maintenance was 1.62 percent and to external electrical energy at optimum power loading was 0.016 percent, a flow analogous to a consumer population.