Experts predict that a worst-case scenario leak of an old oil pipeline where Lake Michigan and Lake Huron meet would cost nearly $2 billion.
The state of Michigan released a draft of a report by an independent team of scientists who estimate that more than half the cost would be cleanup as well as lost tourism income.
The scientists were evaluating the potential impact of a spill from Canadian company Enbridge's Line 5, which runs beneath the Straits of Mackinac.
Enbridge says the pipeline is in good shape and that the report's scenarios are "purely hypothetical." But critics say the 65-year-old line is vulnerable to leaks and should be shut down.
Michigan natural resources director Keith Creagh (CREE) says Line 5 can't remain in its current form.
