Preparation for the mikveh consists of two stages – chafifah (washing) and iyun (inspection). The requirements of chafifah are met by washing all parts of the body. The folds and crevices (e.g. between toes, under breasts) need to be washed in warm water. The hair has to be washed in warm water and thoroughly combed. Please refer to our article on Preparation (Chafifah) for a more comprehensive description of the requirements of chafifah.
Swimming alone does not discharge the obligation of chafifah. It can, however (assuming one doesn't engage in activities that would make one dirty), assure that the body is sufficiently clean that the chafifah process is much faster. It would, for example, be sufficient to take a warm shower prior to mikveh immersion during which warm water is brought to the places mentioned and the hair properly prepared.
Just prior to mikveh immersion the woman must inspect all parts of her body to assure that the Torah requirement of iyun (inspection) is met.