Swimming during a period can be done while using a tampon. Tampons must be used to keep menstrual flow from leaving the body into the water, according to BeingGirl.com.
Pads do not last in the water and deteriorate with too much moisture. Tampons go inside the opening to the vagina, acting as a plug to prevent menstrual flow from escaping. If a tampon is not used while swimming, menstrual flow could escape due to laughing, coughing, sneezing or moving too fast. For sanitary reasons, it is best to replace the tampon with a dry one after swimming, states Women's and Children's Health Network.