Factors Affecting Fluctuations in Extent of Salvinia molesta on Lake Kariba

Soon after Lake Kariba was created by damming the Zambezi River in Central Africa, growth of the aquatic fern Salvinia molesta increased rapidly to cover 1000 km2 of water at the peak infestation of the lake in 1962. Between 1962 and 1972 the area of Salvinia off the southern bank only fluctuated about a figure of 400 km2; and in 1973 it dropped suddenly to 77 km2, and then remained at about this low level. The last survey was made in August 1976 when the area covered was 39 km2. The introduction of the aquatic grasshopper, Paulinia acuminata (Deg.) to Lake Kariba in 1970, its establishment, and its attainment of maximum populations in 1973, probably contributed to the control of Salvinia on the lake.