Residents living near the Mustang Waste Treatment Plant say the smell has been so bad the last couple weeks, it's become unbearable.
Many have complained to the city and to the Oklahoma Department of Environmental Quality.
Some residents say it's hard to come to Wild Horse Park near Mustang City Hall, because just a few hundred yards away is the city's waste water plant that's lately been leaving a pungent odor.
"On it's worst day, it's like you can basically taste it," said Matthew Vann, who lives near the plant. "It smells like anywhere from sewage to something rotting."
Vann said it's hard to breathe some days at home, because it stinks.
"It's been pretty bad just trying to come outside, and even I have a grill and we like to grill and hang out outside, and it's just unbearable sometimes," said Vann, who said he used to blame the smell on his dogs before he knew about the plant.
Not far from Vann's home of two years in the Chisholm Trail neighborhood is the Mustang Waste Water Treatment Plant where all the city's 50 miles of sewage lines end up.
"Despite spending millions of dollars, I'm not sure that you can really make an odor-free plant," said Plant Project Manager Dennis Merrill.
Merrill has worked for the plant for a year but has lived in Mustang for 35 years and says he's placed sodium nitrate in the plant's excess-treatment lagoon to help create algae and break down the foul odor.
But he said the Oklahoma weather conditions haven't helped any.
"Normally, the wind would not be blowing from the plant into their community, but recently, we had some real mild north winds," said Merrill. "That's a perfect way to share offensive odors with the neighbors, and we really truly do regret that."
Vann's wife Erika contacted the Mustang Mayor's office, their homeowners association and the DEQ and learned there were dozens of residents who said they were coping with the same strong smells.
Mustang City Manager Tim Rooney said the city has been aware of the problem for a couple weeks and is addressing it. He said although it's no surprise that a waste water plant would have bad odors in the warm months, the smell has been a greater problem than previous years.
Merrill emailed letters of apology to many nearby residents, explaining the biology of the organic material the plant is dealing with. He said a DEQ official surveyed the plant on Friday.
Merrill said the plant recently entered an agreement with DEQ to increase its capacity by 50 percent in the next years. So, while the plant is now treating 2 million gallons of waste a day, the upgrade will allow it to treat 3 million gallons each day.
But for now, some neighbors are stuck with the stink.
"We have every kind of scented candle and try to keep our home overly fresh as possible to combat the bad smells," Vann said.