Lakes unlike rivers are transient features on the earth's surface and depending on how they were formed, their location and other environmental conditions, they can last thousands of years or just a few decades. Lakes, whether man-made or natural, always go through an aging process. All these factors fit the Weija Lake. Plant nutrients may give rise to growth of aquatic weeds and phytoplanton in a process which is referred to as eutrophication. Weija Lake is considered a highly eutrophic lake.
Algal blooms occur yearly and the aging process is progressing steadily.
There is a yearly cycle of predominantly green algae in the rainy season i.e. from April to July. Diatoms follow in August-October and blue green algae also emerge profusely in the dry season from November to February. All these weeds and algae die and accumulate in the lake. The removal of forest in the catchment area due mainly to farming activity has directly increased soil erosion. Considerable amount of sediment is carried into the lake.