Thousands of creatures have been killed during the unexplained destruction of a “unique little gem” of a nature reserve in south Dublin, conservationists have said.

A parcel of wetland at Sean Walsh Memorial Park in Tallaght, used for decades as a dumping ground for silt, had rewilded itself into a “little miracle” that was home to several protected species, including frogs, newts, eels and bats, according to experts.