I love surfing mostly in ocean. I think the waves in lakes or rivers are too small
Is it even possible to surf in a lake or river?
Yes it  can also be found in lakes or in rivers in the form of a standing wave or tidal bore.
Huh. I never knew that. How long does it take to learn how to surf?
Surfing
Surfing is a surface water sport in which the wave rider, referred to as a surfer, rides on the forward or face of a moving wave, which usually carries the surfer towards the shore. Waves suitable for surfing are primarily found in the ocean, but can also be found in lakes or rivers in the form of a standing wave or tidal bore. However, surfers can also utilize artificial waves such as those from boat wakes and the waves created in artificial wave pools.
The term "surfing"
River surfing
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