A method for cultivating algae can include providing a body of water in a substantially enclosed system. The enclosed system can have a length of channel and a cover. The method can optionally include circulating the body of water through the enclosed system under positive pressure conditions. The positive pressure should prevent ingress of any external atmosphere or material. Further, the method can include cultivating the algae in the body of water at conditions which promote growth. Likewise, a system for cultivating algae can include a channel with a cover, water in the channel, and a pump to introduce positive pressure into the system.