Rowing is a sport in which athletes race against each other on rivers, on lakes or on the ocean, depending upon the type of race and the discipline. The boats are propelled by the reaction forces on the oar blades as they are pushed against the water. The sport can be both recreational, focusing on learning the techniques required, and competitive where overall fitness plays a large role. It is also one of the oldest Olympic sports. In the United States, high school and collegiate rowing is sometimes referred to as crew.