Tsurayuki is referring here to the nagoshi no harae (夏越の祓) purification ceremony, carried out on the last day of the Sixth Month. People would advance to the center of a river and let ritual objects and dolls be carried away by the current, in order to purify themselves of illness and bad fortune. In the capital at the court’s version of the ceremony, special garments were worn, and their sashes were undone at the conclusion of the rite.