Abstract
Crops of macrophytes in three reaches of a chalk stream are recorded Growth was greatest in unshaded regions but was not affected by a sewage effluent discharge (5% of normal river flow). Between March and June net primary productivities of 0.31, 0.47, and 0.85 g organic carbon/m2/day and assimilation efficiencies of 0.19, 0.24 and 0.25% were achieved.