The Minnesota Department of Natural Resources explains that there is no official distinction between streams and rivers, but streams are commonly held to be smaller bodies of water that feed into larger bodies, namely rivers. Both streams and rivers possess currents and are somewhat narrow, or they are at least constrained between two banks.
Despite the lack of an official distinction, there are some accepted ways to classify streams and rivers. In 1952, Professor Arthur Strahler of Columbia University devised a 12-part identification system for streams. According to this system, first order streams, which are often referred to as creeks, are the smallest and shallowest, whereas 12th order streams are the largest and deepest. Bodies of water classified as seventh order or higher are considered rivers.
If multiple streams converge at one point to form a larger, singular body of water, that feature is most often large enough to be a river. The spot at which those streams come together is a confluence.
Despite differences in size, streams and rivers share many similarities. Both typically originate in hills or mountains and can be created due to the melting of a glacier or excessive rain or snow. Both streams and rivers also contribute to erosion by carrying sediment downstream, wearing down rocks and other materials on the banks.