LELYSTAD, Netherlands — The slaughter of thousands of starving animals on a man-made nature reserve has triggered fierce debate about whether it should be regarded as a national treasure or an experiment gone wrong.

More than half of the wild horses, cattle and red deer on the 14,800-acre Oostvaardersplassen didn't survive the winter. Animals within its perimeter must fend for themselves. However, any creatures believed to be suffering are shot by rangers at the site.

Harsh winter weather left piles of dead horses littered around the site. Most of the remains were later removed, but the ghoulish sight of hungry animals just under an hour's drive from Amsterdam led some protesters to cut down fences to free them. Others threw food to the visibly weak animals.

Oostvaardersplassen is now at the center of a lawsuit that aims to prevent a repeat of the carnage in the months to come by allowing more human intervention on the untouched land and relocating animals to other sites.

“I’ve never seen such skinny horses,” recalled Cynthia Danvers, who filed the lawsuit along with her friend and fellow equestrian Annemieke van Straatenafter after visiting in February. “We saw so many dead animals. … It was unbelievable.”

The relatively new park consists of forest, grassland and swamp. The Dutch built dikes to drain the area with plans to use it for industrial purposes in the 1960s. But it was never developed and nature was allowed to take over as an example of "rewilding."

Frans Vera, an ecologist, had the idea to introduce large grazers to control the density of the grasses, reeds and shrubs that were growing. In 1983, 32 Heck cattle, 18 Konik horses and 40 red deer were brought to the Oostvaardersplassen. Generations later, thousands of animals live there.

Endangered birds began migrating to the site early on in the rewilding process and the theory was the large grazers would keep the landscape favorable for them — while still being allowed to run wild.

Konik horses graze in Oostvaardersplassen. Linda Givetash / NBC News

Joke Bijl, a spokesman for the state forestry service Staatsbosbeheer, said the animals are treated as wild and aren’t fed or treated medically to keep the population from growing beyond what the land can support.

But the grazers are watched by rangers to ensure they don’t suffer. “When an animal is stuck in the mud, we help it, and if we see in the early winter or summer a deer has a broken leg, the animal is shot. We don’t leave it to die naturally,” she said.

A lot of animals were shot last winter. In March alone, the park service reported the deaths of 1,155 large grazers, including 157 horses.

No surprise

The grazer population reached an all-time peak of 5,230 last fall. The total deaths for the season topped 3,000. Around 90 percent of the grazers were killed by rangers before they succumbed to the severe conditions.

The carnage didn’t come as a big surprise to the park service. Bijl said the record number of animals there going into the winter meant less food to go around, leaving inhabitants vulnerable.

Then came unfavorable weather.

Ranger Mikal Folkertsma said heavy rain through December turned fields into mud pits, making any remaining grass from the summer inedible.

That was followed by a cold snap in March that brought freezing winds and iced over the ground, leaving already weak animals in worse condition.

Park ranger Mikal Folkertsma checks on animals in Oostvaardersplassen. Linda Givetash / NBC News

There was one night that was particularly bad for deer. “One ranger said, 'Yesterday they were in good condition, they reacted normally, and the next day there were 20 dead' … because it was so cold,” Folkertsma recalled.

Some of the surviving animals gathered near the edge of the reserve, where passersby took notice of their plight.

Danvers and van Straaten, who are heavily involved in the equestrian community, decided to harness the outrage over the animals’ deaths and started a foundation that campaigns for changes in how the reserve is managed.

They want the grazers relocated to a more suitable environment, and in the interim, to be provided with food and better care when necessary. Their Facebook group has nearly 80,000 members, who are demanding that all of the animals be rescued from the reserve.

“We’re going to stop this,” van Straaten said.

A 'reset'

Amid the public pressure, a report was commissioned this year on how to manage the grazers in the future and avoid a repeat of another devastating winter.

The report released this spring recommended a “reset” of the land by reducing the number of grazers to allow the landscape time to rejuvenate from overgrazing. It pegged a sustainable level of large grazers at 1,100 total — about half the number currently living in the area.

But that raises raises the question of how to reduce the population.

While the roughly 200 excess horses can be moved elsewhere, culling the 980 deer required to reach the target number is contentious.

Oostvaardersplassen is a 14,800-acre man-made nature reserve. Linda Givetash / NBC News

“The alternative, to capture the deer and get them on transport, would not be easy and would also put a lot of stress on the deer, so is that the solution? I don’t know,” said Harold Hofstra, a local lawmaker.

Changes to the landscape were also recommended to provide more forested shelter to the animals. This is expected to cost the provincial government up to 15 million euros ($17.2 milion).

The grazers that survived the winter appeared to be thriving during a visit last month. Although unseasonably hot, dry conditions have left the ground hard and shrunken some pools, there were still dense grassy patches where cattle and horses could be found eating and playing.

Nature vs. emotions

To prevent the government from authorizing a cull, Danvers and van Straaten are taking legal action.

Bas Jongmans, their attorney, filed a lawsuit on July 25 asking for a temporary ban on shooting healthy animals, instead forcing the grazers to be relocated.

They also want the government to be held accountable for the welfare of the animals. Jongmans said the government's endorsement of a report that didn’t have a clear solution on how to reduce the deer population was an example of passing the buck. “No one is taking responsibility,” he said.

Jongmans argues that these animals, and the reserve itself, are not truly wild. “If you consider it as nature, you should not put a fence around it,” he said.

Frank Berendse, professor emeritus of ecology at Wageningen University, was Vera's supervisor when he came up with the idea.

Berendse said for the first 15 years the park flourished as anticipated. But as the number of grazers boomed, the vegetation and other species around the park changed.

Konik horses roam around Oostvaardersplassen. Linda Givetash / NBC News

He agrees that the lack of human intervention on the land is a romantic idea that isn’t working practically.

The land is too small to allow for enough diversity of species, such as predators for the grazers, that would achieve a better balance naturally.

“I think it has been a big failure,” he said.

But not all experts see the Oostvaardersplassen as a disaster.

Han Olff, an ecology professor at the University of Groningen, said it’s the perception of horses as pets that is contributing to the outrage.

“They have a special emotional status for people,” he said.

Olff added that the very fact the animal population was able to boom is evidence that the space is suitable for the species living there.

“Death happens when population growth gets to the land’s carrying capacity,” he said. “Would you put a ban on nature on an island?”