Imagine a body of water so vast it could drown the entire contiguous United States under more than a foot of water—this is Lake Superior, the largest freshwater lake on Earth by surface area.
Key Takeaways
- Lake Superior has a surface area of 82,103 square kilometers (31,700 square miles), the largest of any freshwater lake by surface area.
- The lake's maximum length is 563 kilometers (350 miles) from northeast to southwest.
- Lake Superior's maximum width is 257 kilometers (160 miles).
- Lake Superior has a surface area of 82,103 square kilometers (31,700 square miles), the largest of any freshwater lake by surface area.
- Annual average water retention time is 191 years.
- Inflow from 200 rivers averages 350 m³/s.
- Lake Superior has approximately 10,000 species of aquatic organisms.
- The lake supports over 80 species of fish, including lake trout and whitefish.
- Walleye population density is 0.5-1.5 fish per hectare in nearshore areas.
- Lake Superior formed 10,000 years ago post-glacial retreat.
- The basin bedrock primarily Precambrian shield rocks aged 2.5-4 billion years.
- Glacial scouring created the deep basin during Wisconsin glaciation., source isostatic rebound rate 0.3-1.0 cm/year.
- Annual shipping traffic exceeds 60 million tons of cargo.
- Duluth-Superior port handles 40 million tons/year.
- Population around lake: 5 million in watershed.
Lake Superior is the world's largest freshwater lake by surface area.
Ecology
- Lake Superior has approximately 10,000 species of aquatic organisms.
- The lake supports over 80 species of fish, including lake trout and whitefish.
- Walleye population density is 0.5-1.5 fish per hectare in nearshore areas.
- Phytoplankton biomass peaks at 2-5 mg/m³ in summer.
- Deepwater sculpin abundance is highest at depths >150m.
- Sea lamprey control reduced parasitic phase to <5% of historic levels.
- Zebra mussel density reaches 1,000/m² in infested bays.
- Quagga mussel veligers detected at 10-50/L in open water.
- Lake whitefish commercial catch averaged 2,500 metric tons/year 2010-2020.
- Cisco (coregonus artedi) biomass estimated at 100,000 tons lake-wide.
- Diporeia amphipod density declined 90% since 1980s to <10/m².
- Dreissenid mussels cover 20% of benthos >30m depth by 2020.
- Lake trout restoration goal: 2.45 million age-3+ fish.
- Rainbow smelt abundance peaked at 300,000 tons in 1980s, now <50,000.
- Alewife introduced, now comprise <1% of pelagic fish biomass.
- Benthic macroinvertebrate diversity index >3.0 in profundal zones.
- Chlorophyll-a concentration averages 1.5 µg/L oligotrophic status.
- Total phosphorus load target <5 t/km²/yr for oligotrophy.
- Mayfly larvae (Hexagenia) absent due to past pollution, now recovering.
- Bird species: 300+ including migratory warblers using shoreline.
- Piping plover nesting sites: 15 pairs on Wisconsin shores.
- Lake sturgeon spawning runs: 1,000+ adults in Namekagon River.
- Mussel species native: 50, with 20% decline from dreissenids.
- Zooplankton biomass 5-10 g/m² dry weight peak summer.
- Mysis diluviana density 500-1,000/m² at 100m depth.
- Sea trout (splake) stocking: 500,000/year for management.
- Invasive spiny water flea impacts Mysis by 70% predation.
- Amphipod Byblus sp. new dominant post-Diporeia decline.
- Brook trout native, populations in 50+ tributaries.
- Wetland area adjacent: 1,200 km² supporting biodiversity.
- Fish community index of biotic integrity scores 60/100.
Ecology Interpretation
Lake Superior is a vast, complex, and surprisingly resilient ecosystem where the triumphant recovery of lake trout and sturgeon coexists with the silent, smothering dominance of invasive mussels, all held in a delicate and monitored balance.
Geology
- Lake Superior formed 10,000 years ago post-glacial retreat.
- The basin bedrock primarily Precambrian shield rocks aged 2.5-4 billion years.
- Glacial scouring created the deep basin during Wisconsin glaciation., source isostatic rebound rate 0.3-1.0 cm/year.
- Keweenaw Fault runs 200 km along peninsula, active pre-glacial.
- Copper deposits in Keweenaw: 1 billion tons native copper mined historically.
- Lakebed sediments: 70% glacial till, 20% sand, 10% clay.
- Seismic activity: Minor quakes <2.5 magnitude annually.
- Porphyry intrusions host gold mineralization near Marathon.
- Midcontinent Rift underlies basin, 1.1 billion years old, 100 km wide.
- Post-glacial rebound tilts lake level down 1.7m/century eastward.
- Shale gas potential in black shales of Animikie Group.
- Granite batholiths dominate Canadian Shield north shore.
- Volcanic rocks (greenstone) age 2.7 Ga cover 15% basin.
- Fault scarps visible on Isle Royale, drop 100m.
- Lacustrine clays thickness up to 100m in deeper basins.
- Meteor impact craters nearby: Slate Islands (450 Ma).
- Mafic intrusions rich in platinum group elements.
- Karst features limited due to resistant bedrock.
- Sand dunes on south shore up to 60m high, post-glacial.
- Bedrock outcrops: 40% of shoreline exposure.
- Diamondiferous kimberlites intruded 1.1 Ga.
- Glacial erratics weigh up to 100 tons on shores.
- Basin fill sediments total 500 km³ post-glacial.
- Tectonic stability: No major quakes since 1800s.
- Iron formations (BIF) in Mesabi Range supply historic ores.
Geology Interpretation
Lake Superior is a grumpy, ancient elder of a lake, sitting atop a two-billion-year-old geological drama of rifts, glaciers, and copper, all while steadily springing back from the weight of the Ice Age and slowly spilling its tea to the east.
Human Impact
- Annual shipping traffic exceeds 60 million tons of cargo.
- Duluth-Superior port handles 40 million tons/year.
- Population around lake: 5 million in watershed.
- Commercial fishing harvest: 5-7 million lbs/year.
- Tourism generates $2 billion annually.
- Over 200 shipwrecks documented, 350+ estimated.
- Soo Locks passage: 5,000 vessels/year.
- Hydropower from St. Marys: 700 MW capacity.
- Tribal treaty rights for fishing upheld since 1980s.
- Silver Bay taconite plant produces 12 million tons pellets/year.
- Two Harbors ore docks load 15 million tons/year.
- Recreation: 10 million visitor days/year.
- Coast Guard stations: 16 around lake.
- Binational Forum manages binational issues since 2014.
- Phosphorus loading reduced 50% since 1980 via controls.
- Mercury in fish: 20% advisories for consumption.
- Wind energy farms: 500 MW capacity on shores.
- Icebreaking ensures 90% navigation season extension.
- Educational institutions: 20 colleges/universities in basin.
- Cultural heritage sites: 500+ registered.
- Mining legacy: 100 abandoned sites remediated.
- Yacht clubs: 50+ around perimeter.
- Annual regattas: 100+ sailing events.
- Lighthouse count: 71 historic structures.
- Economic value of fishery: $100 million/year.
- Invasive species management cost: $20 million/year.
- Water intake for cities: 1 billion gallons/day.
- Protected areas: 20% of shoreline in parks.
Human Impact Interpretation
Lake Superior is a paradoxical titan, a vast, frigid engine of industry and wilderness where the weight of shipped ore and the ghosts of shipwrecks are balanced by treaty rights, restored shorelines, and the quiet hum of a lighthouse beam.
Hydrology
- Lake Superior has a surface area of 82,103 square kilometers (31,700 square miles), the largest of any freshwater lake by surface area.
- Annual average water retention time is 191 years.
- Inflow from 200 rivers averages 350 m³/s.
- Outflow through St. Marys River is regulated at 2,600 m³/s long-term average.
- Net basin supply (precipitation minus evaporation plus runoff) is about 65 km³/year.
- Water level fluctuates seasonally by up to 0.6 meters.
- Long-term mean outflow is 2,250 m³/s from 1860-2020 data.
- Precipitation over lake averages 762 mm/year.
- Evaporation rate averages 488 mm/year from lake surface.
- River inflow contributes 105 km³ annually on average.
- Residence time for water molecules is approximately 191 years.
- St. Marys River discharge averaged 2,490 m³/s in 2022.
- Lake level in 2023 averaged 176.2 meters (578.1 feet).
- Record high water level was 183.99 m (603.3 ft) on Oct 1985.
- Record low was 175.76 m (576.6 ft) in Mar 1926.
- Annual water balance: P=0.81m, E=0.52m, R=0.23m, O=0.52m.
- Over-lake precipitation is 30% higher than over-land.
- Contribution from Lake Huron backflow is minimal, <5%.
- Runoff coefficient for basin is 0.28.
- Ice cover reduces evaporation by 50% in winter.
- Mean annual range in level is 43 cm.
- Seiches up to 1.5 meters occur due to wind setup.
- Groundwater inflow estimated at 5-10% of total inputs.
- Nipigon River contributes 40 m³/s average.
- Pic River inflow averages 58 m³/s.
- St. Louis River discharge 70 m³/s mean.
- Total direct precipitation input 66 km³/year.
- Lake Superior holds enough water to cover the contiguous U.S. to 1.3 feet depth.
- Average annual outflow volume 71 km³.
- Water renewal time is 174 years based on recent models.
Hydrology Interpretation
Imagine a colossal, stoic freshwater sovereign, its vast 31,700-square-mile realm so immense that a single drop of water, after being greeted by two hundred rivers and serenaded by decades of rain, endures a majestic, two-century-long procession before being granted passage through the St. Marys.
Physical Dimensions
- Lake Superior has a surface area of 82,103 square kilometers (31,700 square miles), the largest of any freshwater lake by surface area.
- The lake's maximum length is 563 kilometers (350 miles) from northeast to southwest.
- Lake Superior's maximum width is 257 kilometers (160 miles).
- The average depth of Lake Superior is 147 meters (483 feet).
- Maximum depth reaches 406 meters (1,332 feet) at a point near the Apostle Islands.
- Shoreline length totals 4,387 kilometers (2,726 miles), including islands.
- The lake contains 2,900 cubic kilometers (2,200 cubic miles) of water.
- Surface elevation averages 183 meters (600 feet) above sea level.
- Lake Superior borders 3 U.S. states (Minnesota, Wisconsin, Michigan) and 1 Canadian province (Ontario).
- The lake has over 30,000 cubic miles of water, holding 10% of the world's surface freshwater.
- Mean depth is approximately 80 meters (262 feet) across the basin.
- The basin covers 127,700 square kilometers (49,300 square miles) total drainage area.
- Lake Superior has 78 named islands larger than 1 square kilometer.
- Total island area within the lake is about 6,600 square kilometers.
- The lake's volume is equivalent to 2.5 quadrillion U.S. gallons.
- Fetch length for waves can exceed 300 kilometers in open water.
- The shoreline is 2,938 miles long excluding islands, 3,046 miles including.
- Lake Superior's surface is at 601 feet (183 m) above mean sea level as of 2023.
- The lake spans latitudes from 46° N to 48° N and longitudes 84° W to 92° W.
- Average width is 160 kilometers (100 miles).
- The deepest point is 405 meters (1,329 feet) in the eastern arm.
- Lake Superior's basin is elliptical, oriented southwest-northeast.
- Total surface area including islands is 82,414 km².
- The lake's perimeter is approximately 1,450 miles for mainland shores.
- Water volume is 12,100 km³ or 2,900 cu mi.
- Lake Superior covers 31,700 sq mi or 82,100 km² precisely.
- The lake is 350 miles long, 160 miles wide at widest.
- Depth at Siskiwit Bay reaches 128 meters (420 feet).
- The Keweenaw Peninsula divides the lake into two arms.
- Eastern basin depth averages deeper than western at 150m vs 100m.
Physical Dimensions Interpretation
Lake Superior is a freshwater leviathan so vast that it could modestly hold all the other Great Lakes plus three extra Lake Eries, yet it remains deceptively serene until it decides to remind you, with a wave born from a 300-kilometer fetch, exactly who contains ten percent of the world's surface fresh water.
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