The Great Lakes are full of shipwrecks and downed planes. Many of the ships are centuries old. The wrecks and their contents are perfectly preserved by the cold, fresh water.

Divers explore these wrecks. Historians and archaeologists study them. They’re a door into the past.

But that door is closing. Why? The ships are falling apart. Invasive mussels are destroying them.  

Opening the gate

Until 1959, the Great Lakes were protected from invasive species. They couldn’t get past Niagara Falls.