Аннотация:Experimentally studied the effect of pH fluctuations in water on the duration of life, photoreaction and swimming speed cercaria Himasthla elongata, Cercaria parvicaudata and Cryptocotyle lingua. It was found that in the range of pH fluctuations from 8.25 to 6.25 with a decrease in pH, the life span of cercariae also decreases. PH fluctuations do not affect the manifestations of photoreactions and the swimming speed of the investigated cercariae.