The Black Tern breeds in loose colonies on nutrient-rich lowland lakes. The nest is a floating platform built of reeds and other plant material, often placed on floating-leaved vegetation such as water-lily leaves or on quaking bogs. The female normally lays 2–3 eggs, which are incubated by both parents for about three weeks. The young are nest-leavers and leave the nest early but are fed by the parents until they fledge. Breeding success depends strongly on a stable water level — heavy rain or falling water levels can flood or expose the nests.