The 22-year-old had entered the water to start a training session near her home in El Tunco when she was struck around 5 pm on Friday, March 19.
Emergency services and medics were called to try to save her, but Diaz was pronounced dead at the scene.
She was training for the upcoming ISA World Surf Games in El Salvador, which she hoped would lead to qualifying for the Tokyo Olympics, the first Games to include surfing.
“A great athlete who has represented our country has left us,” the Salvadoran Surf Federation said in a post paying tribute to Katherine Diaz on social media. “See you soon, great warrior. El Salvador is in mourning.”
The International Surfing Association paid tribute to Diaz in a Facebook post.
“It is with a heavy heart that the ISA has learned about the passing of El Salvador’s Katherine Diaz,” read the statement. “Katherine embodied the joy and energy that make surfing so special and dear to us all, as a global ambassador of the sport.”
“We send our heartfelt condolences to Katherine’s family, the surfers of El Salvador, and to all those in the international surfing community whose lives she touched.”