I believe that is a case of a certain type of eel unique to that lake.

The great lakes have Burbot but they don't really grow past 4 foot at most, hard to mistake them for a giant lake monster.
Also the lakes did get invaded by Sea lampreys but those are just small parasitic creatures that latch into fish in the lakes.

Sturgeon have to be the culprits, they're probably the biggest fish you can catch in those lakes.

There are other things though.

Submarines transporting drugs, guns, people, or other illicit things across the border from Canada or into Canada.
About 20 years ago before the legalization of certain drugs and easy availability it was well known that drugs were being brought into the US from Canada that way.