"The city hall of Ciudad Rodrigo expresses its sadness and presents its condolences for the death of a boy of 13," the municipality said on a Facebook post.
"What should have been a celebration of Spain's team in the football World Cup turned into tragedy," it said, adding that several others were injured.
"A few minutes after 12:30 am local time, rescue services received calls over a fountain collapsing on numerous people," emergency services said in a post on X, adding that another youth had been injured.
Local media reported that the fountain collapsed under the weight of numerous people who had climbed onto it to celebrate Spain's first World Cup victory since 2010 in the football-mad nation.
La Roja defeated Argentina 1-0 on Sunday evening, with Ferran Torres netting the winner in extra time.
FIFA World Cup 2026
The 2026 World Cup took place from June 11th to July 19th in the United States, Canada and Mexico. The tournament featured 48 national teams and was won by Spain, who beat Argentina in the final.
Full schedule and results | Group standings and bracket | Past winners of the tournament | Our team of the tournament | About the 2030 World Cup