River surfing is the sport of surfing either standing waves, tidal bores or upstream waves in rivers. Claims for its origins include a 1955 ride of along the tidal bore of the River Severn. River surfing on standing waves has been documented as far back as the early-1970s in Munich, Germany, today offering the world's largest urban surfing spot. Standing waves In this type of river surfing, the wave is stationary on the river, caused by a high volume of water constricted by flowing over a rock and creating a wave behind. A requirement for this is a flowing water with shallow depth in which the inertia of the water overcomes its gravity due to the supercritical flow speed (Froude number: 1.7 - 4.5, surpassing 4.5 results in direct standing wave) and is therefore neither significantly slowed down by the obstacle nor pushed to the side. It is a form of hydraulic jump. A river surfer can face up-stream and catch this wave and have the feeling of traveling fast over water while not actually moving. River surfing conditions are created by a combination of underlying rock formations and specific water levels, i.e. not too much or too little water. Water flow is usually measured in the SI-unit cubic meters per second (m³/s) (alternatively in liters per second or cubic feet per second). Europe Germany Despite being many hundreds of kilometres from the nearest ocean, Munich has a reputation as a surfing hotspot, offering one of Europe's best waves. The Bavarian capital is the birthplace of river surfing. The city has been the center of surfboard riding on a stationary wave since the early 1970s. Up to 100 surfers daily hit the waves in the city's Englischer Garten, the largest urban park in the world. There, in the river Eisbach, the world's best known river surf spot, the Eisbach wave — literally “ice brook” — the flow velocity of the icy water is about 5 meters per second, at a flow rate of 20 m³/s (equivalent to a mass of 20 tons per second), and the temperature never gets above 15 degrees Celsius. An annual surfing competition is held on the standing wave. Additionally, there are further stationary waves that form on the river Isar just downstream of the Wittelsbacherbrücke bridge in Isarvorstadt, as well as on the canal that joins the Isar channel with the Floßlände. Munich has produced