Nudity
In the United States, male nudity was required when indoor pools were first built at the end of the 19th century. Some were built by city governments, others by the YMCA. In the 20th century, schools began to build pools. Indoor pools were more common in northern states than in the south. Boys and girls had separate classes, so the boys swam nude while the girls usually wore suits. Male nudity was nationwide due to rules from public health organizations about indoor pools. Cleanliness of the pool water was given as the reason. Women's suits were made of cotton, which could be boiled to kill germs. Men's suits were made of wool, which would shrink if boiled. In the early years, fibers from wool suits clogging pool filters was also given as a reason. Bathing suits were allowed only for public competitions. Young boys might be nude while competing in public. Clothed girls and women sometimes attended boys' team practices. Women sometimes coached boy's teams. Male nudity continued until mixed-gender classes were allowed, and slowly stopped in the US when gender equality became law with Title IX of the Education Amendments of 1972. In the 21st century, public male nude swimming is largely forgotten, or denied having ever existed.