Fermentation technology is as old as the history of man. Several foods are produced through fermentation technology. Fufu is produced from cassava through complete submerging of the cassava tuber in water to soften it, which is then sieved into slurry and dewater to some extent and cooked. This study investigated the variations in microbial density and in-situ water quality characteristics of cassava fermentation medium for fufu production. Triplicate samples of raw cassava tuber was obtained from a small-scale cassava processor in Ndemili, Delta state, Nigeria. The peeled cassava tuber was completely submerged in water for 0-144hours. At every 24hours interval the water from the fermentation medium was analyzed for microbial density and in-situ (pH, temperature, total dissolved solid, salinity, conductivity and turbidity) water quality. Results were in the range of 3.13-7.37Log cfu/ml for total fungi counts, 6.08Log cfu/ml for total heterotrophic bacteria counts, 115.80-4347.33mg/l for total dissolved solid, 165.90-10869.07µS/cm for conductivity, 65.50-4347.33ppm for salinity and 33.80-602.67NTU for turbidity, which increased as fermentation progressed. The pH decreased (tending toward acidity) as the fermentation period increased with a value range of 4.67-6.40. Temperature ranged from 28.67-29.20ºC. There was significant variation (p<0.05) between the various period of fermentation except for temperature. The findings of this study showed the variations that occurs during the fermentation of cassava tuber for fufu production.