Dissolved oxygen (DO) is a fundamental indicator of the quality of water in a water body. The higher the DO level in an aquatic ecosystem the better the health of its organisms. DO is not equally distributed throughout an aquatic ecosystem, and all organisms’ oxygen requirements are also not alike. Atmospheric diffusion and photosynthesis are two primary and major sources of DO in aquatic environments. CO2 dissolves in water more readily than O2 with dissolution rates about 200 times more than those of O2. Water in an aquatic ecosystem absorbs oxygen (and other atmospheric gases) until it attains equilibrium at complete saturation. Water temperature and its DO levels are bound in an inverse relationship. DO decreases exponentially as salt levels increase. Dissolved O2 will increase with an increase in pressure. As pressure decreases with an increase in altitude, the waters at lower altitudes will hold more DO that at high altitudes. Microbial activities significantly affect DO levels in water bodies. Accumulation of excessive organic matter in stagnant water bodies can lower DO levels to critically low levels, potentially resulting in hypoxic conditions. BOD and COD are the key parameters in the analysis of the water quality of a water body based on the presence (or absence) of organic pollutants. The higher value of BOD indicates higher oxygen demand for the proliferation and biodegradation action of microorganisms resulting in lower DO levels in the water, which lead to detrimental effects of aquatic life. Since COD encompasses a broader range of O2-consuming substances, COD values of the polluted water are typically higher than BOD values.