Factors influencing on dissolved oxygen level were investigated for suggestion to prevent low dissolved oxygen level by modelling. The laboratory and field study were used to investigate the factors. The processes modelled were consumption and production of dissolved oxygen by algae, reaeration, fish, sediment oxygen demand and wastewater. The rate of production and utilization of dissolved oxygen of factors was separated and later combined for modelling. Subsequently this modelling results were checked with actual dissolved oxygen values at the study site. From the studies, factors influencing increased dissolved oxygen level were algae and reaeration. Factors influencing decreased dissolved oxygen level were algae, sediment oxygen demand, fish, wastewater and oxygen transfer. Primary production and utilization of dissolved oxygen by algae was found to dominate the oxygen balance. The average rate of utilization of sediment oxygen demand was 7.42 mg/(l-m[supurscript 2]-h.), synthesized wastewater was 0.000448 1/l-h and fish was 19.65 mg/l-kg of fish weight-h. The rate of production and utilization by algae varied with chlorophyll-a value. The rate of dissolved oxygen increase and decrease by reaeration and deaeration varied according to the difference in saturation concentration of dissolved oxygen and concentration of dissolved oxygen at any time.
