This lake presents a difficult problem to manage due to its shallow nature and the large inflows of nutrient-rich water.
The water hyacinth. Eichhornia crassipes, is the major pest plant in the lake and its rapid growth is in direct response to the eutrophic conditions existing there. It is neither practicable to reduce nutrient levels, nor to eradicate water hyacinth from the lake. Control is the only avenue remaining.
The aerial spraying of Ametryn by the Ministry of Irrigation has achieved good results, but could be improved by better timing. However, this herbicide is damaging to the phytoplankton in the lake. Precise use of herbicides from a spray boat in conjunction with mechanical methods will alleviate some, but not all. of the water flow and stagnant water problems.
Grass carp, Ctenopharyngodon idella, planned for introduction, will, if used at the appropriate stocking rate, consume most of the submersed vegetation. This would not only increase the fish yield of the lake, but also reduce some of the serious health problems associated with the lake by eliminating the habitat of the intermediate hosts of disease causing organisms.
Phragmites australis is the dominant macrophyte in the ponds. Fortunately the pump station sieves prevent the passage of water hyacinth into the ponds.
The reeds in the ponds can be readily controlled by a combination of:
The feeder canals delivering drainage water to the ponds contain water hyacinth. This plant can be eradicated from the canals by the herbicide glyphosate. This includes controlling the water hyacinth in the old (disused) feeder canal section. Glyphosate is safe to use, in limited quantities, in a fish farm.
There is currently no economic use for water hyacinth. The cost of harvesting far exceeds the intrinsic worth of the plant.
The reed Phragmites australis is locally (Edku region) used for a viable “cottage” industry, such as blinds, fences, temporary shelters and thatching. The young growth is also excellent feed for sheep, cattle and goats.
The quality of reeds in Lake Edku is variable. In the deeper and more saline areas the growth is sparse and the culms are thin and less suited for small industry. The remaining area is probably insufficient for large-scale industry such as paper pulp. Large scale harvesting would probably have a deleterious effect on the lake's ecosystem by opening up water for invasion by water hyacinth.
