CHICAGO (CBS) — People who live near Olive Park on the lakefront are afraid to walk their dogs there now.

As CBS 2’s Charlie De Mar reported, several dogs have come down with a mysterious allergic reaction.

Lying in the shadow of Navy Pier, Milton Lee Olive Park is a dog magnet. It’s where Michela Hattabaugh took her dog, Oshie, on Thursday of last week.

“She deteriorated so fast – that was the scariest part,” Hattabaugh said. “You know, she went from running around, then, you know, just kind of seeming chill, to all of a sudden being unresponsive.”

Hattabaugh knew something was seriously wrong.

“Then she started looking really limp, and I checked her gums and they were completely white – which I knew is a very bad sign,” she said.

Hattabaugh was on the ball. A friend ran the pup to a nearby vet.

“They’re like, ‘Honestly, you got her here right in time,’” she said.

But Hattabaugh said she also learned from the veterinarian that Oshie wasn’t the only dog this week from Olive Park showing similar symptoms.

“They were like: ‘No, there’s something about Olive Park. This is like the fifth dog we’ve seen. You know, one of them actually died,’” Hattabaugh said.

Dr. Amanda Schnitker of the Companion Animal Hospital River North didn’t treat Oshie, but said her symptoms are consistent with an intense allergic reaction.

“An acute anaphylactic reaction can be fatal,” Schnitker said. “Time is really of the essence in these situations.”

Such reactions are sometimes caused by a bee sting, contact with a plant, or ingesting something toxic off the ground.

“Do not stop and call,” Schnitker said. “Just take your dog to the veterinarian.”

Back at Olive Park, Courtney Heath was questioning how to protect her dogs.

“Sometimes I’ll bring them two or three times a day,” she said.

Heath also wondered what could be causing these reactions.

“It’s tough, because it’s like one of the best, you know, green spaces for where we live, but it’s not worth the risk of putting my dog children in danger,” she said.

“People need to know, because there’s just so many dogs there all the time,” added Hattabaugh.