Abstract: A biomass management system using sunlight during the daytime for purifying water having impurities. The biomass management system of the present invention is adapted for use in an impoundment holding water which has an inlet for delivering impure water into the impoundment and an outlet for delivering purified water out of the impoundment. A first type of rooted bottom dwelling plant grows on the bottom of the impoundment and removes some of the impurities in the water. A plurality of elongated channels float on the surface of the water in the impoundment above the bottom dwelling plants. Each of the plurality of the elongated channels are secured in the impoundment in a substantially North-South orientation. Each of the plurality of elongate channels have a holding region with inwardly shaped sides. A second type of floating rootless plant grows in the holding region on the surface of the water in each of the channels and removes some of the impurities in the water.