The importance of phytoplankton in fresh water environment cannot be over emphasized. This study was designed to determine the phytoplankton diversity and abundance in water bodies exposed to different anthropogenic pressures. Water samples were collected from 19 water sources in four categories: Car wash, Municipal wastes, Car wash + Municipal wastes and Drinking water. Phytoplankton species were determined following standard procedures. Palmer’s pollution index was used to evaluate the status of organic pollution. A total of 66 phytoplankton were identified belonging to 44 genera, 34 families and six phyla. There were 52, 32, 11 and 38 species recorded for Car Wash, Municipal Waste, Car wash + Municipal wastes and Drinking water sources, respectively. Nine species cut across the four categories while 22, three and two species were unique to car wash, municipal wastes and drinking water sources, respectively. Nitzschia and Chlorella were the most abundant genera in the different water sources. While phytoplankton abundance correlated positively with nutrients, diversity correlated negatively. The highest and lowest organic pollution indices (24 and 8 respectively), were recorded in the drinking water category. Car wash activity did not only encourage the growth and diversity of algae but also influenced the establishment of unique species, some which are harmful. Human activities in and around water sources in Buea are thus degrading water quality, putting the population at risk. There is therefore need to protect the water resources of Buea.