The Great Lakes are five connected freshwater lakes on the US and Canadian border: Superior, Michigan, Huron, Erie and Ontario. Together they cover 94,250 square miles and hold about 5,439 cubic miles of water, which the EPA puts at 84% of North America’s surface fresh water and about 21% of the world’s supply.
Those totals hide how different the five lakes are. Superior is deep, cold and slow to flush. Erie is shallow and turns its water over in under three years. The table below sets all five side by side so you can see where each one sits.
The five Great Lakes compared in one table
Every figure here comes from the EPA table Physical Features of the Great Lakes. Depths and volumes are measured at low water, and the EPA lists the published references behind its volume figures.
| Lake | Water area | Average depth | Maximum depth | Volume | Retention time |
|---|---|---|---|---|---|
| Superior | 31,700 sq mi (82,100 km²) | 483 ft (147 m) | 1,332 ft (406 m) | 2,900 cu mi (12,100 km³) | 191 years |
| Michigan | 22,300 sq mi (57,800 km²) | 279 ft (85 m) | 925 ft (282 m) | 1,180 cu mi (4,920 km³) | 99 years |
| Huron | 23,000 sq mi (59,600 km²) | 195 ft (59 m) | 750 ft (229 m) | 850 cu mi (3,540 km³) | 22 years |
| Erie | 9,910 sq mi (25,700 km²) | 62 ft (19 m) | 210 ft (64 m) | 116 cu mi (484 km³) | 2.6 years |
| Ontario | 7,340 sq mi (18,960 km²) | 283 ft (86 m) | 802 ft (244 m) | 393 cu mi (1,640 km³) | 6 years |
| Total | 94,250 sq mi (244,160 km²) | 5,439 cu mi (22,684 km³) |
Source: U.S. EPA, Physical Features of the Great Lakes (page last updated August 2026). Retention time is the average number of years water stays in a lake before it flows out or evaporates.
One naming note. The current EPA and NOAA web pages list the easternmost lake as “Lake America.” The water body and every figure are the same, and this guide uses the long-standing name, Lake Ontario.
Why Superior holds more water than the other four combined
Lake Superior holds 12,100 cubic kilometers. Add Michigan, Huron, Erie and Ontario together and you get 10,584 cubic kilometers, so Superior alone carries a little over half of all Great Lakes water.
Depth explains most of it. Superior’s average depth of 147 meters is almost eight times Erie’s 19 meters, and its deepest point reaches 406 meters. A lake that is both the widest and the deepest wins on volume by a wide margin.
Video: TED-Ed
That depth also explains the 191-year retention time. Water entering Superior today will, on average, stay there for close to two centuries. Slow flushing also means a pollutant that reaches Superior is not carried away quickly, which is why the monitoring covered in our Great Lakes water quality report matters more for the upper lakes than the raw tonnage suggests.
Area rank and volume rank are not the same list
This is where most quick summaries go wrong. If you rank the lakes by surface area, Huron is second at 59,600 square kilometers and Michigan is third at 57,800. Rank them by volume and Michigan moves ahead, with 4,920 cubic kilometers against Huron’s 3,540.
Ontario is the other surprise. It has the smallest surface area of the five, yet its average depth of 86 meters means it holds more than three times as much water as Erie. Erie covers more ground but is the shallowest and smallest by volume.
Huron has its own record. Counting its islands, it has 3,827 miles of shoreline, the longest of the five in the EPA table.
The waterways that connect the lakes
The lakes behave as one system because water moves downhill through a chain of rivers and straits from west to east. The EPA drainage figures name the main links:
- The St. Marys River carries Superior’s outflow into Lake Huron.
- Michigan and Huron meet at the Straits of Mackinac. NOAA‘s Great Lakes Environmental Research Laboratory reports a single “Michigan-Huron” lake-wide water level for the pair.
- The St. Clair River, Lake St. Clair and the Detroit River carry Huron’s water down to Erie. Lake St. Clair is small, about 4 cubic kilometers.
- The Niagara River drains Erie into Ontario.
From Ontario, the St. Lawrence River carries the whole system’s outflow toward the Atlantic. Because each lake feeds the next, problems travel downstream. Invasive species spread along the same route, as our report on zebra and quagga mussels in the Great Lakes shows.
Water levels move on more than one clock
NOAA has tracked Great Lakes water levels with reference gauges since 1860. Its water levels page describes a yearly cycle: the lakes are generally lowest in winter and highest in summer or fall, driven by precipitation, snowmelt and evaporation.
Short-term swings can be far larger. Wind and storms can push water to one end of a lake and leave the levels on opposite shores several meters apart for a short time. Shallow Erie shows this most sharply, which is the effect explained in our guide to what a Lake Erie seiche is.
Where the published numbers disagree
Treat any single volume figure as a best estimate. The EPA compares four reference sources, and their Great Lakes totals range from 22,115 to 22,807 cubic kilometers. Erie alone ranges from 483 to 545 cubic kilometers depending on the source.
Shoreline totals have a similar trap. The basin-wide figure of 10,210 miles is larger than the five lake figures added together because it includes the connecting channels. If you quote a number, quote the source with it.
The land draining into the lakes is larger than the lakes themselves. The EPA counts more than 30 million people living in it, and it drains 201,460 square miles of land on both sides of the border.
Great Lakes questions readers ask
Which Great Lake is the deepest?
Lake Superior. The EPA lists its maximum depth at 1,332 feet (406 meters) and its average depth at 483 feet (147 meters), the highest figures for any of the five lakes.
Which Great Lake is the smallest?
It depends on the measure. Lake Ontario has the smallest surface area, at 7,340 square miles. Lake Erie has the smallest volume, at 116 cubic miles, because it is so shallow.
Are Lake Michigan and Lake Huron one lake?
They are separate lakes by name, but they connect at the Straits of Mackinac and sit at the same level. NOAA reports their water level as a single Michigan-Huron figure.
