One has to wonder how the Rusty Crayfish entered the waters of Rainy Lake. One also has to wonder at how fast the crayfish moved out across the lake.
One also must wonder at how the smelt entered Rainy Lake and how it spread across the north basin until it almost was wiped out one fall as the lake overheated and the oxygen was depleted at lower depths.
Zebra mussels, foreign to North America, have invaded the Great Lakes and many of the tributaries that run into the system. Asian carp are another invasive species that's gradually making its way across North America.