Assessing the distribution of macrophyte population in Lake Naivasha Kenya; using GIS & Remote sensing to inform management

Exotic aliens, Salvinia molesta (floating water fern) and Eichhornia crassipes (water hyacinth) encroachment in Lake Naivasha are associated with deteriorating water conditions.The study aims to map the extent and distribution of macrophytes and other aquatic invasive weeds in lake Naivasha, Kenya. High-resolution Earth Observation (EO) data (Sentinel-2 acquired on 28th February 2015, 20th March 2025) and in-situ data were used to assess the extent of macrophytes and other Aquatic invasive weeds in lake Naivasha, Kenya. The images were geo-referenced and geographically rectified. The datum was set to WGS 84 and referenced to Universal Transverse Mercator (UTM) zone 36 North. Image compositing using both false and natural colour band combinations was conducted including image enhancement, and clipping to the extent of the study area. The image interpretation was done at a scale of 1:50000, while ground truthing was undertaken to provide supplemental details of actual information in the field. Maps were produced and the macrophytes quantified in terms of distribution and coverage using different spectral signatures. Kappa Index of agreement was used to assess the accuracy of the maps .

Multi temporal analysis of the satellite images showed that the area covered by water hyacinth had increased significantly between the study dates. The overall findings indicate that the coverage of papyrus remained relatively stable from 570 Ha to 590 Ha . while the areas under water hyacinth has consistently increased from (940 Ha) to (1480 Ha) both in terms distribution and coverage. There is need for government to develop and implement appropriate aquatic weed control strategies, enforce policies and regulation on pollution control and management strategies including communities sensitization on effects of pollution on the fresh water ecosystems