Data on seasonal biomass variation and productivity data based on short-term incubation experiments are presented for three species of macrophyte algae. The difficulties inherent in estimating annual productivity of benthic macroalgae are discussed, and a methodology is presented which combines field data obtained for biomass and production rates, data on the tidal regime of the study area and data on the variation of photosynthetically active radiation in a computer simulation of macrophyte primary productivity. The estimated annual productivity obtained for the three species is compared, and the differences between estimates using this approach and simple harvesting methods are examined. The application of studies of this nature in assessing the role of the macrophytobenthos in the mass balance of pollutants in estuaries is discussed, with reference to nutrient uptake.