President Barack Obama has signed into law a ban on bringing bighead carp into the U.S. They are among two Asian carp species threatening to infest the Great Lakes.

The measure signed Tuesday adds bighead carp to a list of wildlife that cannot be imported or taken across state lines. The only exceptions would be for scientific, medical or educational purposes and would require a permit.

Bighead and silver carp have infested waterways in the Chicago area. Authorities are trying to prevent them from getting into the Great Lakes, where they would compete with native fish for food.

Silver carp are already on the banned list. Democratic Sen. Carl Levin of Michigan says the crackdown on bighead carp is an important step in limiting the spread of the unwanted fish.