A housing development on a Cardiff beauty spot could be threatened after people opposed to the plans discovered examples of rare mushrooms there.
A number of different types of wax caps have been found
Campaigners fighting plans for luxury homes and a nature reserve at Llanishen Reservoir have found evidence of a rare fungi called the waxcap.
The group say 29 species of fungi are on the site. It wants the Countryside Council for Wales to investigate.
The developers say they have carried out a study on the mushrooms.
Residents have been campaigning against the proposed development by Western Power who want to reduce the 60-acre reservoir to one of 10 or 11 acres, and build luxury homes on its banks.
It has also proposed preserving nearby Lisvane Reservoir and creating a wetland habitat to be maintained by a wildlife trust.
But local people say the site should be preserved as it is.
There are plans to develop Llanishen reservoir
They say that the discovery of the wax caps mushrooms is another reason for the site to be saved.
Dr Richard Cowie, a member of the Llanishen Residents Action Group (Rag), said: "It is fantastic to find such an important site for fungi in the middle of Wales' capital city.
"The site is special because of the wide range of species of wax caps, which are found all around the embankments of the Llanishen reservoir.
"To lose just one species from the site would be a tragedy.
"The reservoir embankments could provide a fantastic resource for teaching youngsters about the importance of wildlife and grassland conservation," he added.
The developers say that protecting the species is important to their plans
Dr Cowie said that he hoped that the Countryside Council for Wales would look at the site and declare it a site of special scientific importance.
A spokesman for Western Power said that the company had carried out an environmental study on the wax caps growing in the area.
"Waxcap protection is an important part of our scheme," he said.