In the below Envisat image (acquired on 6 March 2010) North America’s three lakes are pictured. Snow cover is evident across the land, and we can see ice build-up along some of the lakes’ edges. Lake Erie is the fourth largest lake (by surface area) of the five Great Lakes in North America, and the tenth largest globally or twelfth largest globally if measured in terms of surface area. Covering an area of over 244 000 sq km and containing about 22 600 cubic km of water, together the Great Lakes form the largest connected area of fresh, surface water on Earth. The only place where more fresh water is contained is in the polar ice caps.
A green algal bloom is also visible in Lake Erie. These toxic blooms have been a problem for the lake in recent years. Caused by heightened levels of phosphorus – found in fertilisers and common household products – finding its way into the water, these blooms have increased the size of the lake’s low-oxygen ‘dead zone’.
They have played an important role in North America’s economic development by providing a transportation system between the agricultural and mining regions on the western shores with the market centres on the East Coast. The ability to ship materials such as coal, iron and ore also gave rise to the steel and automobile industries in the area. Detroit – nicknamed ‘Motor City’ – is located on the Detroit River (lower left). Envisat image courtesy ESA.