Water Hyacinth Infestation in Ponds and Satellite Lakes in the Lake Victoria Basin on Tanzania: Status and Efforts to Manage it.

Abstract

A survey was conducted in ponds and satellite lakes in the lake Victoria basin in March 2000 to ascertain the presence of water hyacinth and its effect to the communities and the environment. Out of 14 (12 ponds and 2 satellite lakes) surveyed, water hyacinth was found in 11 ponds (i.e. 91.7% of ponds) and there was no water hyacinth in the satellite lakes under study. The highest (31.5 ha) infestation was recorded at Ngulyati pond in Bariadi, Shinyanga followed by Bukabwa (8 ha). No water hyacinth was found at Sarawe pond, Itabagumba and Buswahili satellite lakes. Plant population varied significantly (P< 0.001) with the highest (196 plants/0.25m2) recorded at Bukabwa and the lowest (21/0.25m2) at Bunda ponds. The immediate effect of the water hyacinth infestation in the ponds included difficulty in accessing water for domestic use owing to the extensive water hyacinth mats and loss of water through evapotranspiration. In the efforts to control the weed, water hyacinth weevils’ Neochetina eichhorniae and N. bruchi were released in 7 of them (9,600 adult weevils in 5 ponds at Mwanza Prison Center and 44,000 and 52,600 at Bukabwa and Ngulyati ponds respectively) which have established and multiplied to a level of up to 8 weevils per plant causing feeding scars of 38.65 on average at Ngulyati. Weed population decreased significantly (P<0.05) owing to the insect-induced stress. Other dominant aquatic weed species found growing in the ponds included Ceratophylum dermesum, Pistia stateotes, Rapa natas and Brasenia SP at Buswahili Satellite Lake and Cyperus spp and Justicia spp in the rest of the ponds and Satellite Lake. The presence of water hyacinth in the ponds and satellite lakes has partly contributed to water hyacinth regrowth (resurgence) in lake Victoria and other water bodies in the lake basin. Therefore management strategies of water hyacinth in Lake Victoria should also include ponds and satellite lakes.