Minerals drop out of the river when the flow slows. Alluvial deposits can form deltas where the river flows into a lake or ocean. Farms and cities have been developed on large deltas. New Orleans sits on the delta formed where the Mississippi River flows into the Gulf of Mexico. Other heavily-populated deltas include those of the Nile in Egypt and the Mekong in Vietnam.
Some communities depend on the fish that live in or travel along rivers.
Transportation Navigable waters carry much of the world's heavy trade by ship and barge. The Yangtze, Mississippi, Volga, St. Lawrence, Hudson, Delaware, Rhine, and Thames Rivers are among the most heavily-trafficked, connecting major ports. Rivers can also be barriers to land transportation. They can be crossed by ferries, bridges, and tunnels. Because of the difficulty of crossing rivers, they have sometimes become territorial boundaries.