“Before the 1920s, swimming pools in the North were segregated along gender lines but not racial ones.

This changed as they became gender integrated.
Racial stereotypes around cleanliness and safety, as well as intense fears of Black men interacting with White women in bathing suits, turned pools into some of the most segregated public spaces in America.”

https://www.cnn.com/2023/07/22/business/public-pools-extreme-heat/index.html

I did not know the first part of this history.