Olympics organizers were urgently investigating why several venues had swathes of empty seats on Saturday, the first full day of competition at the London Games.

Organizers LOCOG were overwhelmed with demand for Olympics tickets when they first went on sale more than a year ago.

But there were rows and rows of unoccupied seats at some venues Saturday, notably the Aquatics Center and the Wimbledon tennis complex, causing fans to vent their fury outside venues and on social media.

The embarrassing sight was blamed on accredited bodies, which include the International Olympic Committee, sponsors and the media.

“We are aware that some venues have empty seats,” a LOCOG spokesman told AFP. “We believe the empty seats are in accredited seating areas, and we are in the process of finding out who should have been in the seats and why they weren’t there.”