DULUTH — The spread of spiny water fleas to another Minnesota lake highlights how an invasive species can spread.

Scientists believe the foreign species crossed the ocean in the ballast water of saltwater ships. They’ve been confirmed in Lake Superior since 1987, and now the Department of Natural Resources confirms they’ve reached Shagawa Lake near Ely.

DNR aquatic invasive species specialist Rich Rezanka said more than 50 Minnesota lakes and rivers are now infested.

Spiny water fleas disrupt the food chain because they compete with small fish for plankton.

When populations are high, anglers can experience frustration with masses of spiny water fleas clogging fishing lines and other water equipment. So it’s critical that anglers remove them and avoid transporting them to other waters.