The lesser swamp warbler or Cape reed warbler (Acrocephalus gracilirostris) is an Old World warbler in the genus Acrocephalus. It is a resident breeder in Africa from the Democratic Republic of the Congo, the Chad and Ethiopia south to South Africa. This is a common species of reedbeds in standing water.
The lesser swamp warbler is a plain-coloured smallish bird 14–16 cm long and weighing around 20 g. Its upperparts are rich brown, and it has a white supercilium. The underparts are white, with a rufous wash to the flanks. The long, strong bill has a slightly down-curved upper mandible; it is blackish-yellow with a yellower base. The legs are blue-grey and the eyes are brown. Adults of both sexes and juvenile birds are very similar in appearance.
The song is rich and melodious, a series of bubbly phrases that include trilling notes, cheerup chee trrreee and a large number of variations, with pauses between phrases.