Oceans to Lakes

Chicago skyline from Lake Michigan


What does Lake Michigan have in common with the ocean? The contrasts seem obvious: freshwater vs. saltwater, size, species, smell, etc; however, there are a few surprising commonalities this Great Lake shares with the ocean.


Believe it or not, Lake Michigan has reefs; Milwaukee reef, Julian’s reef and Wilmette reef, just to name a few. Although they may not resemble The Great Barrier Reef, these rocky limestone habitats are equally important to fish and other lake dwelling organisms.

What about limestone? Between 443 and 358 million years ago (the Silurian and Devonian periods), Lake Michigan was a warm shallow reef filled with creatures like sea scorpions and armored fish. Evidences of the old reefs remain in the form of bedrock, boulder and cobble. Even Michigan’s state rock, the Petoskey stone, is comprised of fossilized coral. The rocky reefs form 3D structures that are critical habitat for native species of perch, lake trout, and bass, especially as they face overfishing and invasive species.

Invasive Species 

Over 180 invasive/non-native species have infiltrated the Great Lakes, including Lake Michigan. Invasive species are often spread via ballast water, which is upheld and discharged by cargo ships. Species have even hitched rides from the Caspian Sea in ballast tanks, some subsequently invading the Great Lakes. Other species, such as the sea lamprey, invaded through the man-made canals and waterways created for ships to travel between the Great Lakes and the Atlantic Ocean.

Sea lampreys are one of the top invasive villains in the Great Lakes. Originally native to the Northern Atlantic, the jawless, eel like fish is known for causing sudden, dramatic shifts to foreign ecosystems. Due to the co-evolution between lampreys and their native food sources, the blood sucking parasites do not typically kill their hosts. However, only about one in seven fish species in the Great Lakes survives after being parasitized by a lamprey. In the past, Lampreys had such a drastic impact on lake fish populations that annual lake trout harvests decreased from 15 million lb to 300,000 lb, for lakes Huron and Superior. Since then, sea lamprey control programs have proven effective, though eradication is highly unlikely.


Lampreys aren’t the only “sea” villains to occupy Lake Michigan. There were pirates! Prohibition-era booze pirates, fur trade pirates, lumber pirates, and religious pirates roamed the waters of Lake Michigan.

The most notorious pirate was Dan Seavey, or Roaring Dan. Roaring Dan was a bar brawler, bootlegger, smuggler, poacher, and pimper – supposedly the only pirate to be officially charged with piracy on the Great Lakes.

Roaring Dan’s most infamous account occurred June 11, 1908, when he stole a small schooner, the Nellie Johnson. Federal authorities responded by conducting a manhunt across Lake Michigan on a 178 ft. steel hulled gunboat. Needless to say, he was caught and brought to Chicago in iron chains. Although Dan was arraigned for mutiny and sedition on the high seas, the grand jury never indicted slippery Seavey.

There you have it! Prehistoric coral reefs, Sea Lampreys, and Sea-vey pirates. Freshwater and saltwater may have their differences, but for those of you lucky enough to live near Lake Michigan, enjoy your “ocean”.



Silurian reefs

Petosky Stone

Invasive Species in the Great Lakes 

Sea Lampreys

Non-native Invasive Species 

Roaring Dan Seavy by Dr. Richard J. Boyd

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