Beginning of autumn can't go in the water. Why not?

Beginning of autumn can't touch water. It is said that after beginning of autumn, autumn began, the temperature difference between day and night began to increase, and the temperature difference between the surface temperature and the deep temperature of natural water also increased. Swimming at this time is easy to catch a cold, and in severe cases, swimming cramps may occur.

Beginning of autumn is the thirteenth of the twenty-four solar terms, and it is the beginning of autumn. The bucket refers to the southwest, and the sun reaches the longitude of 135, and it is celebrated on August 7 or 8 of the Gregorian calendar every year. "Reason" means the beginning; "Autumn" means that the grain is ripe. The change of the whole nature is a step-by-step process, and beginning of autumn is a turning point in which the Yang gradually closes, the Yin gradually grows, and the Yang gradually gets cloudy.