Zürich is divided by a river and > 6 km lakeside labyrinth of small streets in the old city. Since 1992, Zürich hosts the street parade, which is the biggest event in Switzerland and one of the biggest in Europe. It is an event of techno parties, and nearly one million people gather along the lake and the old city. Medical assistance is provided by the emergency system of Zürich in cooperation with the fire department, police department, as well as the emergency systems of the neighborhoods, civil protection, and Volunteers. This mass gathering is unique because almost 16 km2 of the city and old city and four of the six bridges that connect the two sides of the city are closed and dedicated to the Streetparade, which complicates rescue operations. Since it is impossible for an ambulance to get to injured persons in the crowd, and very difficult to transfer patients to a hospital, many stationary medical units and two boats are used in the city, each with a combination of emergency doctors, paramedics, firefighters, and volunteers, who also can build mobile units and an advanced medical unit in a shelter that has rooms for 108 patients. Every mobile unit has a GPS system that permits the Operational Headquarters to have an overview. This system has been helpful in this particular event, permitting medical personnel to reach the injured persons in short time and to treat the majority of the patients in situ, minimizing the necessity of transport. In 2010, 680 patients were treated 680, of which, only 42 were transported to a hospital. No deaths due to panic attacks of lack of emergency response have occurred in the past 19 years.