Spennymoor Town Council has been accused of "environmental vandalism" for allowing horses to graze on the town's nature reserve.
Complaints have been received by the council and Groundwork East Durham by people who feel the horses have destroyed part of the Cow Plantation over the summer.
Peter Walton, who lives in Wood Vue, next to the woodland, said the horses had trampled part of the nature area and polluted the marsh section with their manure.
"It was all wild plants and flowers, and they have turned part of it into just mud," he said.
"It was beautiful before with all the wildlife and insects, and now it's just been destroyed. They have churned it up and eaten the plants - it's environmental vandalism."
The Cow Plantation became a nature reserve in 1994 and has been plagued by vandals and fly tippers in the past.
Councillor Joan Wood, a member of Spennymoor Town Council's cow plantation sub-committee, said if the horses did not graze on part of the site, the shrubs and meadow grasses would take hold and the amenity would be lost to walkers.
She said: "What the town council has got to do is make sure that piece of land is there for everybody. If you don't control the meadow grasses they will strangle the smaller plants."
But Coun Wood said: "I know we do have a problem with the horses at the moment. I feel they have been grazed at the wrong time of the year, and we do need some monitoring of it."
She said the council was awaiting a report into the effect of the horses on the land before deciding what action to take.
Tracy Colling, local Agenda 21 project officer with Groundwork East Durham, said she had received numerous telephone calls complaining about the horses.
But she said the group was waiting for an ecological study to be carried out by Durham Wildlife Services, to assess the impact of the horses, before reporting back to the town council next month
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