Collective. The Water Tower hosted the exposition Water for life where "audiovisual media and lighting play a key role in the way the contents are communicated". Aquarium This thematic pavilion, which remained in operation after the expo, is the biggest freshwater aquarium in Europe, with 300 species of fauna from rivers around the world in 60 tanks or terrariums. Rivers represented are: The Nile: It contains species of the great African lakes. It also has crocodiles and an exhibition on the Mediterranean and the Red Sea. The Mekong: In this river visitors will find species of the Himalayas, gardens from the river's lower course, the Pacific Ocean and coral reefs. The Amazon river: It is divided into three different areas. The first of them is the Amazon jungle with its coconut trees and mangroves. The second area is about the Amazon forest while the third area is the mangrove swamp with an exhibition on the Atlantic Ocean. The Murray-Darling river: This exhibition begins in the flooded regions and goes through desert areas. It finishes with a video exhibition about birds. The Ebro: It is also represented in two areas. The first area is a mountain cave and the second is the course of the river. There will also be an exhibition on the Mediterranean Sea. The "World River": It represents the past, when "all the continents were united as a single island surrounded by ocean". Thematic squares Thirst This thematic square employed mirrors, audiovisual projections and combinations of light and sound to create optical illusions. It was 46.7 metres in diameter, covering a total area of 1,640 square metres (820 of them were the exposition area). Igloo of salt Designed by Cloud 9 / Enric Ruiz-Geli, this plaza's architecture was that of an enigmatic building. It was an inflatable structure covered with salt that reflected the sun's rays and lit up at night as if it had stored all of the necessary energy to continue to function. This themed plaza was designed according to Expo Zaragoza 2008's sustainability criteria: the use of PVC was avoided in electrical wiring, as well as tropical wood, synthetic varnish or solvent-based paints; taps made use of water-saving systems. Additionally, the frame was hired out to avoid having to demolish it once the expo was complete. The use of EFTE in the building's three-layered roof made air conditioning unnecessary. One of the EFTE layers was