What is the hottest body of water in the world?

The Great Lakes have the "largest surface area of fresh water" in the world. The National Oceanic and Atmospheric Administration (NOAA) reports that the combination of Lake Michigan-Huron (technically considered to be one lake by many geologist) has a surface area of aproximatly 45,300 square miles (22,300 square mi for Lake Michigan and 23,000 square mi for Lake Huron).

However, if you are asking about the "largest body of fresh water" (by volume) in the world, that would be Lake Baikal located in Russia. Lake Baikal has more water because of it's depth (over 5000 ft at it's deepest) and thus makes it technically the "largest body of fresh water" in the world.

Here is a breakdown of the water volumes and surface areas for the Great Lakes (from NOAA) and Lake Baikal for comparison. Note that if you combine all the Great Lakes together, Lake Baikal still has more water by volume.

Lake Superior

- volume: 2,935 cubic mi

- surface area: 31,700 square miles

Lake Michigan

- volume: 1,180 cubic mi

- surface area: 22,300 square mi

Lake Huron

- volume: 849 cubic mi

- surface area: 23,000 square mi

Lake Erie

- volume: 116 cubic mi

- surface area: 9,910 square mi

Lake Ontario

- volume: 393 cubic mi

- surface area: 7,340 square mi

Total volume for all great lakes combined = 5,473 cubic miles

Total surface area for all great lakes combined = 94,250 square miles

Lake Baikal

- volume: 5,521 cubic mi

- surface area: 12,200 square miles