Rowers in San Juan rowers club celebrate the winning of 'Kontxa flag Challenge'. San Juan rowers won their 5th 'Kontxa consecutively. Donostia (Basque Country). September 9. 2018. This Challenge is one of the oldest and most famous rowing races along the Bay of Biscay, held annually in the Kontxa bay. It takes place on the first two weekends in September and regularly draws crowds of people. Men's challenge was first held in 1879. Since 2008, women rowers have their challenge. (Gari Garaialde / Bostok Photo).