Consumers Energy says a tugboat anchor caused more than $1 million in damage when two underwater power lines were severed in April.
The utility is the latest to file a lawsuit over the April 1 incident in the Straits of Mackinac near the Mackinac Bridge.
Enbridge Energy, the state of Michigan and the owner of other power lines are also suing VanEnkevort Tug and Barge, claiming damage.
Consumers Energy has ruled out any other vessel striking its power lines at that time.
The company says the "no-anchor zone" is well known.
The lawsuit was filed last week in federal court in western Michigan.
A spokesman for the tugboat company declined to comment Monday.
