Lake Levels

Dynamic Great Lakes

Water levels in the Great Lakes have always been highly variable. Seasonal variation occurs every year as the lakes rise an average of 12-18 inches from winter to early summer. Long-term fluctuations may last for years, decades, or longer.

Lake levels fluctuate over time in response to wind, storms, precipitation, evaporation from the lakes’ surfaces, and runoff from tributaries. Each Great Lake responds to these factors in unique ways, depending on the size and composition of the lake’s watershed, total volume of the lake basin, and other characteristics. The lakes also influence each other’s levels, as they are all interconnected. Dredging and erosion in key river channels, such as the St. Clair and Detroit rivers, can also alter the flow of water through the Great Lakes basin. Finally, flow regulating structures give humans some control over water levels at key strategic points in the basin. These structures are carefully regulated by the International Joint Commission.

Spanning more than 3,200 miles of Great Lakes shoreline, Michigan’s coastal communities and economies feel the effects of lake level fluctuations, including:

  • Stranded or flooded docks and boat ramps
  • Erosion damage to shorelines and structures during high water periods
  • Disruptions to navigation, energy production, and drinking water supply
  • Damage to coastal infrastructure and habitats

Living with uncertainty

Right now, scientists aren’t sure how climate change will affect Great Lakes levels. Warmer air will allow more water to evaporate from the lakes, particularly when wintertime ice cover is limited or absent. But computer climate models also suggest that the Great Lakes basin will experience more rain and snow, which could offset the effects of higher evaporation. Whatever happens, the reality is that weather, climate, and lake levels will continue to fluctuate. It’s important for coastal communities to expect and prepare for these ups and downs.

When levels fluctuate much above or below the long-term average, the impacts can be significant, especially in highly developed areas where infrastructure was not designed to withstand changing levels. Strategic community planning can mitigate the impact of fluctuating lake levels on the boating industry and other coastal-dependent businesses by taking appropriate steps:

  • Use updated rainfall data when designing new infrastructure.
  • Use planning and zoning power to regulate floodplains, coastal land use, placement of structures, and shoreline protection structures.
  • Remove dams to restore natural floodplain processes.
  • Conduct assessments to identify properties and infrastructure vulnerable to flooding, erosion, and lake level changes.
  • Adjust placement of lake-based water intake pipes.
  • Revise loading and unloading policies for cargo ships.
  • Update dredging plans and needs
  • Upgrade road/stream crossings.
  • Stabilize stream and river banks.

Resources