There is no difference between men and women in terms of swimming. Everybody can swim as long as their private parts are covered. The private part of women is their body as a whole except their face, hands and feet. Their private part against other women is the part between knees and belly. Men’s private part against both women and other men is the part between knees and belly.
Allah the Almighty commands:
“Tell the believing men to reduce some of their looks and cover their private parts, because that is purer for them. Verily, Allah is All-Aware of what they are trying to do. Tell the believing women to reduce some of their looks and cover their private parts. Tell them not to uncover their private parts except what is naturally seen.” (The Light 24:30-31)
Consequently, women who cover their body as a whole can swim in public places. Women who cover between their knees and belly can swim while they are not in the sight of men.