The 911 call came at 5:17 p.m. Shots fired in the Coleman Center at Western Technical College.
Police descended immediately. As nervous students were evacuated from nearby buildings, officers armed with assault rifles took up defensive positions. Others stormed inside with weapons drawn, searching room by room for the gunman.
Then they found the balloons.
A class was popping them as part of a school project, and a student mistook the noise for gunfire and called police.
The false alarm tonight highlights rising tension on college campuses in the wake of the Newtown school massacre, Boston Marathon bombings and other mass shootings.
"I thought I was going to see some guy with a gun behind them," said Alexandra Hoida, 19, a student who was on the Western campus when police swarmed.
She and others evacuated the nearby Kumm Center and waited outside during the search.
The police response was so intense, she said, it made her fear the worst.
Morgan Hoff, 19, also was evacuated from Kumm.
"Everything that's been going on," Hoff said. "That was the first thing that came to my mind."
It’s the second time in a month police have responded to a potential gun situation on a La Crosse college campus.
A mentally disturbed student at the University of Wisconsin-La Crosse was arrested April 19 after bringing a shotgun into the college's science building. Professors quickly ushered students into classrooms and locked the doors as police searched for the student. He was found in a parking lot with the unloaded gun.
The same week, Carroll University in Waukesha, Wis., initiated a campus lockdown in response to reports of a student with a gun. A SWAT team, an armored vehicle and the FBI also responded, but the weapon turned out to be similar to a BB gun.
Though that case and the Western incident turned out to be false alarms, police and college officials say it’s always better to be safe than sorry.
Police searched every room in the Coleman Center even after finding the balloons, just in case there was still a shooter hiding inside.
And for students, a heightened awareness of danger seems to be the new norm on college campuses.
Many UW-L students said their first thoughts were of the Boston Marathon bombings when they heard about the student with a gun on campus last month.
"I don't blame the other student for calling the police at all," Western spokeswoman Julie Lemon said this evening after police had left. "You can't be too careful in these situations."