A Turkish-born couple in Switzerland was fined for keeping their daughters out of coed swimming lessons at the public school back in 2008.
They cited a religious exemption and appealed the fine (worth about $1,380), but the European Court of Human Rights rejected that appeal Tuesday. The court ruled the school didn't violate the family's freedom of religion.
The court said the school "interfered" but that public schools had a "special role" in integrating newcomers.
It's not the first time Islamic rules and swimming have caused controversy in Europe.
Last year, Switzerland fined another man for refusing to let his daughter swim during school hours. In Germany in 2013, a judge ruled that a girl must attend swim classes, but let her wear a burkini, a garment that a French town briefly banned.
The Swiss school offered to let the girls in the case wear burkinis, but their mother said that "didn't erase the contours" of their bodies and thus would not satisfy the religious restrictions.