Dog owners in the Mission and Bernal Heights area say their pets have gotten sick after visiting Precita Park last week.
They suspect that it may be the result of chemicals in a fertilizer used by city workers to treat the grass.
The San Francisco Recreation and Parks Department spokeswoman says they received two reports of dogs getting sick.
She says no fertilizer has been used here recently, but that the Department is looking into what could have sickened the dogs.
Precita Park is a popular playground for dogs.
"This is a beautiful park. It's well- used and it's cared for," says Johnnie Thompson, a dog owner.
"It makes me really concerned. We live around the corner. We're here 3-4 times a day, "says Thompson.
"My dog has gotten sick a couple of times. But I don't know if it's because of the park or not," says Chris Johnson, the owner of Cubby, a Pomeranian Pekingnese mix.
Thompson says he'd like to find out more about what workers are using to treat the grass.
When asked if he'll visit the park again, he replied, "God, I got to think about that."
Connie Chan with Rec and Park says recently, the Department has roped off newly seeded areas with standard grass mix that should not have any negative effect on humans or animals and that no fertilizer has been used in well over a year.
In a written statement, she said, "We are still looking into our maintenance activities last week and would welcome any input from the public on any incidents that they might have witnessed."
"I've been coming to this park for 20-25 years with dogs. Every time the park service has done something with fertilizer or mulch or whatever they're gonna do, they post it," says Karen Kircher, a dog owner.
She says she suspects it isn't chemicals, but garbage left at the park that could have sickened the dogs.
"Dogs love to dig into that stuff. Someone could have thrown it thinking it was a good spot for their trash and dogs got into it," says Kircher.
Dog owners want answers.
"Pretty concerned. Vidar [a Corgi] is pretty prone to getting sick especially since he's a puppy," says neighbor Alex Howard.
"I'll definitely keep myself informed as to what’s happening," says Thompson, owner of a mini Schnauzer.
Rec and Park says workers will be inspecting the park this week to see if they can identify any potential hazards that could be related to the two incidents of dogs getting sick.
Most neighbors tell KTVU they'll continue to visit the park with their dogs, but keep a closer eye on their pets.