There is a water area in the centre of the town, the "Ilmenauer Teichgebiet". This lies between the old town and the main campus of the university with 5 lakes, laid out by monks during the Middle Ages for providing fish. The biggest lake with an area of 95 hectares is made up of the Wipfra river next to Heyda district by the Heyda Dam, built in the 1980s. Nearly all the unbuilt municipal area is covered by forest with spruces and pines (in the north) as the main species. Smaller areas are also covered by beeches. The forest monocultures of spruces were caused by the enormous need of wood for mining and glass industry during the previous centuries. However, they are susceptible to diseases and windthrow and will be replaced by more natural mixed forest during the next few decades after storm conditions Kyrill led to enormous damage within the town's forests in 2007.