Abstract: Regression formulas relating water retention period to oxygen consumption. and contents of inorganic nitrogen and phosphate in a shaded dolphin pool are presented. The time exponent of the consumed oxygen is 0.2285. The diel increasing coefficients of ammonia, nitrate are 0.327 and 0.2468, respectively, while the nitrite is in the range of 0.397—0.539. The diel increasing rate of phosphate is 0.2—0.6. To improve living condition for the dolphin, it is necessary to regulate the NO2-N content in the pool water not higher than 0.1ppm, although the residual chorine in supplied tap water was found harmless to the animal.