Hellabrunn Zoo (or Tierpark Hellabrunn in German) is a 40 hectare (99 acre) zoological garden in the Bavarian capital of Munich. The zoo is situated on the right bank of the river Isar, in the southern part of Munich near the quarter of Thalkirchen. As the groundwater level here is rather high and the water is of very good quality, the zoo can cover its needs for freshwater by using its own wells. A high ratio of enclosures are cageless, relying upon moat features to keep the animals in place. The zoo was the first zoo in the world not organized by species, but also by geographical aspects. For example, the wood bisons share their enclosure with prairie dogs. In 2013, the zoo was ranked 4th best zoo in Europe (up from 12th). It focuses on conservation and captive breeding rare species such as the rare drill and silvery gibbons. Also gorillas, giraffes, elephants, wood bisons, elk and Arctic foxes were successfully bred in the zoo, which houses a large number of species. It is one of the very few zoos that allows visitors to bring dogs. Tierpark Hellabrunn is a member of the European Association of Zoos and Aquaria (EAZA) and the World Association of Zoos and Aquariums (WAZA) and participates in the European Endangered Species Programme (EEP).