Many people doubt the city's official story about why police closed North Avenue Beach on Monday. (Credit: CBS)

CHICAGO (CBS) — Police have been blaming hot weather on Monday for the sudden evacuation of North Avenue Beach.

But as CBS 2’s Pamela Jones reports, two days later, a lot of residents and beachgoers still are not buying the city’s version of events.

They want to know, why weren’t all the beaches closed on Monday?

Mayor Rahm Emanuel is now asking for a report on what went down, but he’s standing by the decision to close.

Meanwhile, city officials are sticking to their story about collapsing beachgoers who were sick from the heat pushing people to close North Avenue Beach around 6 p.m. on Memorial Day.

“You had public safety and you had public health,” Emanuel said. “There’s no Monday morning quarterbacking.”

“There was no gang activity that was involved in the commander’s decision to close the beach,” said police Supt. Garry McCarthy.

But a police source close to the situation tells a different story. That officer says police got reports of up to 1,000 suspected gang members meeting here to start trouble.

Callers to Cliff Kelley’s show on WVON-1690 AM agree.

“It was gangbangers acting stupid up there,” one caller said.

“It’s a very plausible argument that there were gangbangers up there,” another said.

When asked if most of his callers feel like they are not being given a straight story about what happened at North Avenue Beach, Kelley said no.

“All of them” feel that way, he said.

People at the beach Wednesday wee mixed on the truth about why the beach closed.

“I don’t know of any gang-related stuff happening toward North Avenue,” one beachgoer said. “I didn’t see it.”

But most agreed hostility had to play a part.

“There was a lot of, like, ethnic minorities, like, yelling at each other,” one woman said.

“The violence that they had between each other, I guess quarrels, and they knew that everyone would meet here,” a man said.

McCarthy said there needs to be a better plan about how to handle large crowds, so emergency crews can get through to people who need help.

He says that was a major concern that day, whatever else might have happened. There were several outbreaks of gang violence in cities across the country.

The announcement about a safety-related closure came over the public-address system shortly after 6 p.m. Monday. A firefighting crew sprayed crowds with a mist of water from a 2 1/2-inch hose as beach-goers made their way from the lakefront.

In all, four people were rushed to area hospitals from the beach as a result of heat-related illness. One was even listed in critical condition.

But violent flash mobs have been a concern at North Avenue Beach previously.

In April at the beach, sources say a group of about 100 teens surrounded two people on bikes. Both were knocked off their bikes and thrown into Lake Michigan.