On a side road near the South Platte River in Denver, a woman stepped out of a white pickup with a bag full of cat food, about to commit an act that some say is charitable and others think perpetuates a growing problem.

Denver is home to an estimated 100,000 feral cats, and people across the city have become kitty-cat caregivers — putting out food in alleyways, building shelters and taking the wild animals to the veterinarian.

This “it takes a village” philosophy for cats is not embraced by everyone.

Battles between residents caring for “community cats” and their neighbors who see feral cats as a public health concern are becoming more and more common.

“I don’t want my last name in the paper. I don’t want people coming after me,” said the woman, who allowed that her first name is Susan, as she emptied the bag into a ceramic bowl on the roadside.

Every few days, Susan drives to the same spot off of Santa Fe Drive with food and water for a colony of about 10 stray cats that is being looked after by a host of other people in the neighborhood.

The riverbank near Grant-Frontier Park on the Denver-Englewood border is lined with tins of cat food delivered by strangers and homemade cat houses filled with straw for bedding.

Colonies such as this one are spread throughout metro Denver.

“This is a terrible eyesore,” Kat Lovato said about the cat colony. “We can’t walk our dogs in the park in the evening because these cats have brought in these huge coyotes. And there are skunks.”

Complaints about cat colonies have reached unprecedented levels, said Lorraine Pacheco, an officer with Denver’s Animal Care & Control.

“It’s almost as bad as the barking dogs,” she said.

Last week, Pacheco was called to a neighborhood meeting because one woman feeding alley cats was irate at another woman who has been trapping them in her newly renovated backyard and hauling them to the pound.

“Both sides are passionate,” Pacheco said.

Doug Linkhart, manager of Denver’s Environmental Health, called feral cats “a huge problem” for the city.

“Our shelter and others are having to euthanize thousands of cats every year, partly because of feral cats and their interaction with domestic cats,” he said. “Beginning sometime next year, we will implement a major initiative, working with other local animal organizations, to spay and neuter as many feral cats as possible to help control this population.”

Across the country, urban areas are struggling with what to do with the proliferation of stray cats.

Some say the problem is linked to general pet overpopulation. Others believe the feral-cat population has swelled with the failing economy.

People abandoning foreclosed homes or getting kicked out of apartments are more apt to leave behind the cat than the family dog, said Sherri Leggett, operations director for the Feline Fix, a nonprofit providing affordable and accessible spay and neuter surgeries for cats.

“People have a higher regard for dogs than cats,” she said.

Cat advocates say the humane option for cats that cannot be domesticated is to trap, neuter, vaccinate and release them back into the wild with ongoing supervision by a “colony manager.” It is a course of action advocated by the Humane Society and the Colorado Veterinary Medical Association.

“What caused the problem in the first place is someone abandoned that cat, and that cat started having kittens,” Leggett said. “It is a community problem that was created by humans. If you trap them and neuter them, the procreation stops. The population is static, and over time it will decrease.”

Others, particularly bird conservationists, advocate keeping all cats indoors and are opposed to trapping, neutering and releasing.

“We see cat advocates spending millions in the public advocacy for (trapping and releasing),” said Steve Holmer with the American Bird Conservancy. “But feral cats, they don’t belong in the environment.”

Free-roaming cats are decimating bird populations, attracting predators and carrying diseases that can cause birth defects and serious health problems in humans, he said.

“We don’t see the colonies ever disappearing,” said Holmer, adding that colonies only draw more cats as people see them as perfect dumping grounds.

While the colonies grow, he said, birds will be the biggest victims.

The American Bird Conservancy estimates cats kill 500 million to 1 billion birds every year in the United States. He also said coyotes are drawn by the easy pickings, leading to more interactions between coyotes and other pets and people.

“Cats are a non-native pest,” said Jeff Birek, outreach biologist with the Rocky Mountain Bird Observatory in Fort Collins. “Even though they are cute, they are causing ecological damage.”

The only option with adult feral cats is to trap them and put them down, he said.

“No one likes to stomach that idea,” Birek said. “It’s not an idea that many people want to talk about, but putting them back out in the wild is one that we are paying for in spades.”

Nevertheless, municipalities across the country are pushing for people to trap, neuter and release cats rather than having them impounded in the city’s shelter — where it can cost the city $75 to $150 a cat.

In Denver, the number of cats being impounded in the city’s shelter has been steadily declining for five years, from a high of 2,841 in 2007 to 2,119 so far this year.

The drop is likely because of sterilization efforts and because people are trapping, neutering and releasing cats instead of bringing them into the shelter, said Pacheco, the animal-control officer.

The Feline Fix, along with Divine Feline mobile clinic, has spayed or neutered 22,000 cats since 2003. The group charges a subsidized fee of $20 for the surgeries and vaccinations. It also asks people to register that they will be caretakers for the colony.

Last week, the group began a year-long program to offer free spay and neuter surgeries for every cat in Denver’s 80205 ZIP code — the Cole and Whittier neighborhoods of Denver, where an estimated 5,000 cats live.

Whenever Feline Fix spays or neuters feral cats, it vaccinates them for rabies and distemper. It also clips the tip of the left ear to identify the cats that have been fixed.

“We try to educate people about continuing to care for them even after they are fixed,” Erica Rambus, medical director for Feline Fix. “People who are complaining should understand that this is not the fault of these cats. These animals are the product of human irresponsibility.”

People shouldn’t litter, dump cat food or throw turkey legs out for cats, like at the Platte River site. But they should continue to care for the animals, she said.

Several minutes after the small ceramic bowl was filled with cat food on the banks of the South Platte, a rustling could be heard in the bushes. A flash of gray and white was seen behind the green leaves. A healthy-looking gray-and-black striped cat with a white mane and yellow eyes crept out. No one has yet trapped and fixed this group of cats.

The cat circled his camp, warily watching the strangers who quietly tracked his movements. He sniffed the food and quickly darted back into the brush.

“A lot of people care about them,” said the woman, holding an empty cat-food bag. “They are harmless and aren’t hurting anyone.”

Jeremy P. Meyer: 303-954-1367 or @jpmeyer@denverpost.com