More than 700 miles of Great Lakes shoreline potentially vulnerable to Straits of Mackinac oil spills

Study published by University of Michigan Water Center.

Researcher Dave Schwab illustrated the potential danger of a possible oil spill at the Straits of Mackinac using computer modeling to show how the oil quickly spreads to Lake Huron, and Lake Michigan, contaminating shoreline areas miles away from the Line 5 pipeline.

  • Enbridge Line 5

    Line 5 splits into two 20-inch-diameter pipes to cross the Straits of Mackinac, just west of the Mackinac Bridge.

  • Enbridge Line 5

    Originally designed to last 50 years, the now 63-year-old pipeline moves up to 20 million gallons of light crude oil, light synthetic crude oil and natural gas liquids across the straits each day.

About the Study

  • Schwab ran 840 simulations of a release from the Enbridge Line 5 pipeline under the Straits of Mackinac. His computer model used weather and water-current data measured in the straits during the ice-free season. Three spill volumes were considered: 5,000 barrels (210,000 gallons), 10,000 barrels (420,000 gallons) and 25,000 barrels (1.05 million gallons).

Selected Simulation Cases

Animations of particle trajectories for 3 of the cases illustrate the wide variety of conditions encountered during spring, summer and fall in the Straits. In the animations, the oil tracer particles are shown as black dots. A magenta dot represents a beached particle. The legend in the animation indicates the amount of time that has elapsed since the beginning of the case, the percent of particles that have beached, and an estimate of the length of shoreline.

  • Case 2 Video Thumbnail

    Case 2

    The initial oil patch in this case moves quickly southeastward into Lake Huron for 6 hours, but then reverses direction and moves back into the southern part of the Straits while depositing oil along the southern shoreline both east and west of Mackinaw City. After 1 day, over 60% of the oil has beached and impacted 15 km of shoreline. In the next 12 hours, 30% more has beached and 22 km of shoreline are significantly affected. This case illustrates how quickly a spill could impact a large amount of shoreline.

  • Case 3 Video Thumbnail

    Case 3

    This case starts only 2 days after case 2, but has a vastly different outcome. Oil initially moves northeastward toward St. Helena Island in Lake Michigan, and doesn’t reach 90% beached until day 40 when 90 km of shoreline are impacted. Note: This case starts only two days after the previous case.

  • Case 5 Video Thumbnail

    Case 5

    In this case, oil moves almost exclusively eastward, with more than 30% of the oil beached on Mackinac Island, Bois Blanc Island, and almost the entire Lake Huron shoreline from Mackinaw City to Cheboygan after 3 days. The oil travels as far south as Presque Isle on the Lake Huron shoreline in 15 days, and a small percentage of the particles reach northern Saginaw Bay on day 30. This case also illustrates the some of extreme distances in Lake Huron that could be reached in 30 days.

Compelling Results

  • A total of 720 miles (1,162 km) of shoreline are considered potentially vulnerable to Straits of Mackinac oil spills. This map shows the probability that beached oil concentrations would exceed the threshold needed to trigger shoreline cleanup following the release of 25,000 barrels at the Straits of Mackinac.

  • iPhone Thumbnail
  • iPhone Thumbnail
  • This map shows the percentage of cases in which oil is present at a given location at any time after a Straits of Mackinac release.

Study and full story available at


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