Complex sentence: It disappeared from the Treur River in the 1960's, but during the 1970's it was rediscovered in the upper Blyde River, an area that received National Heritage status in 1985.
Split into simpler sentences: It disappeared from the Treur River in the 1960's. During the 1970's it was rediscovered in the upper Blyde River, an area that was proclaimed a National Heritage Site in 1985.