The youngest female champion swimmer in a national swimming competition currently well-documented is Yu Zidi from China. She is only 12 years old and achieved remarkable success by winning and setting record times in events at the Chinese national championships and competing impressively at the 2025 World Swimming Championships. Specifically, Yu Zidi recorded the fastest ever 200 IM time by a 12-year-old swimmer and won a silver medal at the 2025 Chinese National Swimming Championships, making her the youngest national champion in recent history.

Other young swimmers like Gretchen Walsh and Summer McIntosh have made significant achievements at young ages but are older (early to mid-teens) compared to Yu Zidi. For example, Summer McIntosh is a notable young champion but was 14 during her first Olympic recognition, older than Yu Zidi's 12 years.

Thus, the youngest champion female swimmer in a national swimming competition as of 2025 is Yu Zidi, age 12.