Intertidal seagrasses and macroalgae were studied at a sewage-polluted beach (Ocean Road) and a control site at Kunduchi beach, with a view to assessing the effect of sewage discharge on macrophyte species composition, abundance and above-ground biomass. A total of six species of seagrasses were recorded at Ocean Road of which two, Thalassia hemprichii and Cymodocea rotundata were the most abundant. Eight species of seagrasses were recorded at Kunduchi. Two species, Syringodium isoetifolium and Thalassodendron ciliatum were dominant in areas with strong oceanic influence. Halodule wrightii and Halophila ovalis were widely distributed in the two study areas. The mean biomass of seagrasses between Ocean Road and Kunduchi beaches was not significantly different (z = 4.053; p = 0.001; d.f. = 54). A total of 25 and 24 macroalgae species were recorded at Ocean Road and Kunduchi beaches, respectively. The total biomass of macroalgae was higher at Ocean Road than at Kunduchi (t = 4.838; p>0.001). While the biomass of brown macroalgae was higher at Kunduchi (t = 2.115; p = 0.039), that of red algae was similar at both sites (t = 1.986; p = 0.052). Of the 11 epiphytic species of macroalgae recorded on T. ciliatum at Kunduchi area, 73% were red algae, 18% green algae and 9% brown algae. The dominant species on this beach was the brown alga Cystoseira myrica. It was concluded that elevated levels of ammonium at Ocean Road is a likely cause of the observed higher biomass of green macroalgae at this site.