Completar frases Team Together 3Versión en línea Do all rivers go into the sea? por Yuliia Smoliana 1 sand source mountain flow mouth valley waterfalls river tributary When it rains , the rainwater runs into a on a hill or a . The start of a river is called its . Rivers then or run down into a valley . Some rivers make a lake in the . Some rivers have a . A tributary is a smaller river . It flows into the big river . Some rivers have more than one tributary . Rivers can also have and rockpools in them . Big rivers sometimes have an island in them . Rivers then flow into the sea . This place is called the of the river . In very hot countries , some rivers dry up in the and can ? t go into the sea .