Preliminary experiments indicate that waterhyacinths and a water‐fern (Azoilasp.) show enhanced growth in CO2‐enriched atmospheres. Waterhyacinths were subjected to a range of nutrient conditions, and plants exposed to an enhanced CO2‐atmosphere showed weight gains under all conditions; control plants lost weight at low and medium nutrient enrichments.Azolla, a plant that is sensitive to light intensity, was subjected to a range of light conditions. Plants exposed to ambient conditions lost weight under medium and high light intensity and gained weight under low light intensity conditions. In contrast,Azollain CO2‐enriched atmospheres had increasing weight gains under all light conditions studied.