A system (1) for growing green algae. The algae are contained in a liquid which, in this embodiment, is water. System (1) includes four successively linked alternately directed substantially parallel and coextensive open channels (3), (4), (5) and (6), for directing a first flow (8) of the liquid. Four successively linked alternately directed substantially parallel and coextensive open channels (11), (12), (13) and (14) direct a second flow (15) of the liquid. The second flow (15) is derived at least in part from the first (flow 8) and the first flow (8) is derived at least in part from the second flow (15). Three successively linked alternately directed substantially parallel and coextensive open channels (22), (23) and (24) direct a third flow (25) of the liquid. The third flow is derived from the second flow (15) and, in channel (24), at least some of the algae are removed from the liquid.
