A flow passage (70) is shown in the form of two successively linked, substantially parallel, adjacent, open top channels (12A, 14A) to form part of an algae cultivation system. The forward flow of the water passes in sequence through the respective open top channels (12A) and (14A) of flow passage (70), in the direction of arrow ‘；A’； and then is then recirculated back into to the channel (12A), and so on. The combination of added nutrients, sunlight and agitation of the fluid flow encourages the growth cultivation of the biological organisms which are continually suspended in the flowing water. Such a flow passage (70) can be used as a standalone passage used as part of a system for cultivation of biological organisms, or it can also form one basic unit of a modular system which is arranged in use to have several such flow passages linked together in use. Such a reconfigurable apparatus gives the user the flexibility to cultivate different algae products both separately and simultaneously.
