Historians race against time — and invasive species — to study Great Lakes shipwrecks

The Great Lakes' frigid fresh water used to keep shipwrecks so well preserved that divers could see dishes in the cupboards. Downed planes that spent decades underwater were left so pristine they could practically fly again when archaeologists finally discovered them.

Now, an invasive mussel is destroying shipwrecks deep in the depths of the lakes, forcing archeologists and amateur historians into a race against time to find as many sites as they can before the region touching eight U.S. states and the Canadian province of Ontario loses any physical trace of its centuries-long maritime history.

"What you need to understand is every shipwreck is covered with quagga mussels in the lower Great Lakes," Wisconsin state maritime archaeologist Tamara Thomsen said. "Everything. If you drain the lakes, you'll get a bowl of quagga mussels."