The early explorers of North America used lakes and their connecting rivers as their chief travel routes. Some of these explorers paddled canoes up the St. Lawrence River to the Great Lakes. Steamboats took the place of canoes as the civilization of white people expanded. Today, freighters, tugboats, and barges work their way along inland navigation routes on the Great Lakes, carrying raw materials to the industrial cities that are located along the lakes. Products carried on the Great Lakes include coal, iron ore, and grain.
Lakes provide an important source of water for irrigation.
Water may be fed from the lakes to farmers' fields by ditches or canals, or it may be pumped into an overhead system of sprinklers. People have built huge dams on rivers in desert areas to create reservoirs of water for irrigation. The Egyptians built the Aswan High Dam on the Nile River partly for this purpose. These irrigated regions, which lie mainly in Pakistan, supply food for millions of people. Water supply has been a serious problem ever since people started to live in towns and cities.