Mira Minde Polje and related Springs. 02/12/05; Região Lisboa e Vale do Tejo; 662 ha; 39°29'N 008°38'W. Natura 2000 site, Natural Park. A subterranean hydrological system based on the polje, or flat, closed depression draining underground, situated in the country's most important limestone karstic region and part of the recharge area of the two most important karstic aquifers and karstic springs in Portugal. The flooding episodes with very high fluctuations of groundwater level are a rare example in the West Mediterranean biogeographic region. TheAlviela spring is one of the deepest in the world and is locally connected to a cave complex that represents the most significant fluvio-karstic phenomena in Portugal, one which supports several bat colonies with more than 5,000 bats in total. The Almonda spring is related with the most extensive Portuguese cave, an important Paleolithic site. The area features important habitat types under which temporary ponds, natural eutrophic lakes, and tall humid grasslands are the most abundant. Adverse effects are mainly caused in some places by water pollution, urban and industrial developments, and increasing tourism. There are educational activities at the underground interpretation centres in the Pena and Almonda Caves as well as the interpretation centre and Cave Bats Observatory at the Alviela Springs, which welcome up to 100,000 visitors per year. Ramsar site no. 1616. Most recent RIS information: 2006.