Abstract: An apparatus for cultivating macrophytes grown on the water surface in a circular basin structure containing a channel of plant growth nutrients water spiraling from the basin structure periphery into the center of the basin structure and then back out again to the periphery. Two spiraling berms, constructed in parallel, define the single, continuous channel of water. A conveyor means is mounted on a rotatable arm that extends from the basin structure center to the basin structure periphery and rotates about the central support. The conveyor means moves laterally along the rotatable arm so as to remain in the center of the channel of water as that arm rotates. A portion of the floating macrophytes on the water surface is harvested one or more times each day and transported to beyond the periphery of the basin structure where the floating macrophytes are available for subsequent processing.