The Phase II of the NRBP was conducted on the Ngong/Motoine river to provide information for the assessment of a pilot project to identify major point sources of pollution.

Garbage along Ngong River

The NRBP-Phase II monitoring and assessment (Seasonal Assessment) collected useful data and developed a sampling strategy for the other rivers. Baseline data collection for Phase II was conducted by NETWAS in conjunction with the Nairobi City Council.

The Baseline study results for the Phase II from 20 sampling stations, indicated existence of self-purification mechanisms taking place from the first sampling stations, as well as a significant decrease in the pollutants and turbidity as the water passes through several dams. Within the Nairobi dam, pollutants and turbidity decrease due to the retention of water and its slow movement, and a great deal of sedimentation taking place within the dam.

Downstream of the Nairobi dam, turbidity increased rapidly and heavy metals concentration also increased downstream of the Nairobi dam. The COD and BOD5 decreased steadily up to the confluence with Nairobi River, supporting the claim that some self-purification or dilution or both were taking place but their levels were still high above the limits recommended for natural waters.

These observations were based solely on water analysis as no analysis was conducted on the biota and sediments. It was recommended that full chemical analysis be conducted on the sediments and selected biota to determine whether the elements that appear to have reduced in concentration have actually been removed from the biotic system through uptake or adsorption mechanisms.

After the baseline study, several questions still remained unanswered and it was recommended that additional work be conducted on the rivers to investigate the fate of polluting substances in the general aquatic ecology. It was recommended that sediment be sampled and analysed during the Seasonal Assessment.

The University of Nairobi (UoN) represented by CIPL signed a Memorandum of Understanding with UNEP to continue on the Phase II of the Pollution Monitoring and Assessment in the NRBP. Among other tasks the UoN consortium was to undertake in the project were collect and analyze (laboratory) water and sediment quality samples.