Enteromorpha clathrata, a marine seaweed, can be grown in shallow ponds with an exchange of water once in several days to maintain salinity within tolerable limits. rn fertilized conditions growth is rapid, 28 g dry weight m(2) day. This is less than the highest rates reported for other algae, but other systems have used CO2 supplementation or large water volumes to supply inorganic carbon. Enteromorpha clathrata, unlike other algae that have been studied, gives high yields without CO2 supplementation. We have measured the effect of pH and salinity on productivity and determined tolerance ranges of temperature, salinity and pH. The implications for the feasibility of Enteromorpha culture in seawater-irrigated ponds are discussed. The ability to conduct highly productive agriculture in areas that are now desert through seawater irrigation will provide a new resource for feed, food and biomass.