Seoul Mayor Oh Se-hoon poses for a photo with Sium Sium Hangang Triathlon Festival participants at Ttukseom Hangang Park in Gwangjin-gu, Seoul, Sunday. (Yonhap)

Seoul Mayor Oh Se-hoon swam across the Han River on Sunday as a participant in a triathlon festival planned by the city government, praising the water quality and encouraging people to enjoy the city's beloved river through water activities.

According to the Seoul Metropolitan Government, the mayor, clad in a full-body wetsuit and swim cap emblazoned with the slogan, “Seoul My Soul,” joined around 2,000 other swimmers in the 1-kilometer swim on the second day of the 1st Sium Sium Hangang Triathlon Festival at the Ttukseom Hangang Park in Gwangjin-gu.

"Although it was my first time swimming across the river and it felt longer than I expected, the water was unbelievably clean," Oh said, after completing the swim in about 30 minutes.

Held from Saturday to Sunday, this non-competitive event was designed for Seoulites to experience the scenic river at their own individual pace, participating in swimming, cycling and running courses offered at both beginner and advanced levels.

The mayor, known as a sports enthusiast, also completed the 20-kilometer advanced cycling course and a 10-kilometer run on Saturday.