Lake Chiuta and the surrounding plain is drained by the Lugenda river, which is part of the Ruvuma River drainage system. Lake Chilwa, about 35 km (22 mi) south of Lake Chiuta is unusual as it has no outlet although when it overflows it flows into Lake Chiuta through a swampy plain. High rates of evaporation ensure that the lake seldom fills up – much of the lake is only 1 metre deep or less.