This book presents contributions devoted to the hydrogeochemical characterization of aquatic environments of Patagonia, including those of Ushuaia city, known as "The southernmost city in the world". Patagonia (between 39° and 55° S) is located in southern South America. Eight main river systems pour their waters into the SW Atlantic Ocean. Rivers, with their headwaters mainly located in the Andes, supply dissolved and particulate matter to the coastal zone, as well as nutrients, which benefit biological communities. Besides, freshwater in this region with little anthropogenic impact supports human life and a high wildlife biodiversity. Unfortunately, the recent increase in human activities, such as the use of fertilizers, wastewater discharges, extensive deforestation and dam construction, is affecting the quality and quantity of water resources. The book is of interest for researchers, professors and government agencies that decide on water resources management policies.