The potential for14C‐fluometuron(N,N‐dimethyl‐N'‐[3‐(trifluoromethyl)‐phenylurea]) degradation in unialgal cultures of 15 strains of green algae and 2 species of cyanobacteria (blue‐green algae) was investigated. Eight of 15 algal strains(Ankistrodesmus, Chlorella, Pediastrum, ScenedesmusandSelenastrumspecies) metabolized fluometuron viaN‐demethylation to desmethyl fluometuron. The highest fluometuron‐demethylation activity was observed in the generaAnkistrodesmus (A. falcatusandA.cf.nannoselene)andSelenastrum (S. capricormitum, S. gracileandS. mimitum)with complete sequential demethylation to trifluoromethylphenylurea observed in certain strains. Low levels of fluometuron‐demethylating activity in certain algal strains may be due to herbicide toxicity. Algal strains(AnkistrodesmusandSelenastrumsp.) that metabolize fluometuron viaN‐demethylation also transform the herbicide atrazine (6‐chloro‐N‐ethyl‐N‘’‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine) byN‐dealkylation to deethylatrazine, however this activity is several‐fold lower than fluometuron‐demethylation activity. Our study indicates that algae have the potential to contribute to herbicide transformations in aquatic environments viaN‐dealkylation transformations.