"We have been working very hard to keep the intergrity of the banks."
Wire mesh, corrogated iron and bits of wood have been put across the stream, at the point where the reserve meets private property, by someone to try and stop cattle getting into the reserve.
Kāpiti Coast District Council parks and recreation manager Alison Law said, "We have spoken with the owner of the cows and will be working with him to make sure this can't happen again."
Mr Palmer, from Waikanae, said cattle in the reserve had been an ongoing issue.
The solution to the problem was "proper fencing".
Mr Palmer, who is in his 80s and spends one day a week working in the reserve, was one of the original people who helped create the reserve in the mid 1990s.
Throughout the years many people, including school children, have spent countless hours transforming the area into a thriving ecological environment.
Greendale Reserve, which covers 3.5ha, is a Forest and Bird environmental restoration project developed in partnership with Kāpiti Coast District Council supported by Greater Wellington Regional Council.