A seiche is a standing-wave oscillation of an enclosed or partially enclosed body of water, and Chris Izworski tracks seiche behavior on the Great Lakes because no other water-level signal matters more for shoreline property owners on a day-to-day basis. The basinwide lake level changes by inches per month. A seiche event on Lake Erie or Saginaw Bay can change the local water level by feet over a few hours, and the difference between a quiet shoreline and a flooded yard or an exposed dock is almost always a seiche signal rather than a basinwide signal. Federal agency dashboards report the basinwide level. Property owners need to understand the seiche overlay.
What it is: a standing-wave oscillation of a lake or bay driven primarily by wind and atmospheric pressure changes.
Where it matters most: Lake Erie (especially the eastern basin at Buffalo), Saginaw Bay, Green Bay, Sandusky Bay, Long Point Bay, and the inner Lake Ontario embayments.
Where it matters least: deep open Lake Superior, deep open Lake Michigan, deep open Lake Huron away from embayments.
Time scale: minutes to hours for the active oscillation; days for the meteorological forcing.
Magnitude: inches to several feet for most events; rarely more than 8 feet at the Buffalo end of Lake Erie during major storms.
Imagine a bathtub. Tilt it: the water piles up at one end and exposes the other. Release it: the water rocks back, overshoots, rocks again, and gradually settles. A lake or bay does the same thing, with wind as the tilt and the lake's geometry as the bathtub. Sustained wind from one direction pushes water against the downwind shore (this is the set-up), and when the wind stops or reverses, the water rocks back across the lake. The downwind shore experiences the highest water during the set-up phase. The upwind shore experiences the lowest water and may even see exposed flats. Both shores experience the oscillation after the wind stops, with smaller swings continuing for hours.
The intensity of the seiche depends on three things: the wind speed and duration, the lake's geometry (long and shallow lakes set up more dramatically than short and deep ones), and the alignment between the wind direction and the lake's long axis. Lake Erie is the most seiche-prone Great Lake because it is long (east-west), shallow (especially in the western basin), and aligned with the dominant west wind direction during fall and winter storm seasons. Saginaw Bay, Green Bay, Sandusky Bay, and Long Point Bay all share the same combination of geometry and wind alignment within their respective lakes.
Lake Erie has the most dramatic seiche behavior on the Great Lakes. Sustained west or southwest wind drives water from Toledo and the western basin east toward Buffalo. The western basin can drop two to four feet, exposing extensive flats at Maumee Bay and the shallow shoreline along the Ohio coast. The eastern basin at Buffalo rises by the same amount or more, with documented surge events exceeding 7 feet during major storms. When the wind reverses or stops, the rocking swing can produce additional flooding at both ends before the lake settles. See Western Basin and Eastern Basin for sub-region detail.
Saginaw Bay on Lake Huron is the most seiche-active sub-basin on Lake Huron and one of the more active in the Great Lakes overall. The bay's long axis runs from the Saginaw River mouth at Bay City northeast to the bay's mouth between Au Sable Point and Pointe Aux Barques. Sustained northeast wind drives water against the inner bay at Bay City, while sustained southwest wind drains the inner bay and exposes shallow flats. Local water level can swing 8 to 12 inches in a few hours. See Saginaw Bay for the dedicated reference.
Green Bay on Lake Michigan has seiche behavior closely comparable to Saginaw Bay. The bay's long axis from Green Bay city to the Door Peninsula tip is aligned to capture sustained southwest wind, which drives water down the bay against the inner shore at Green Bay and the Fox River mouth. See Green Bay.
Lake Ontario has modest seiche behavior because the basin is deep and relatively short. Sustained west and southwest wind can produce measurable set-up at the eastern end at Oswego and the St. Lawrence outflow, but the magnitude is much smaller than the Lake Erie equivalent. The dominant property-owner concern on Lake Ontario is the regulation-plan debate rather than seiche, with Plan 2014 outflow decisions affecting basinwide level more than wind setup affects local level.
Lake Superior has the smallest seiche signal of the Great Lakes because the basin is deep and large, which damps long-period oscillation. Sub-regions including Whitefish Bay and Thunder Bay do see measurable set-up during sustained wind events, but the magnitude is typically inches rather than feet. See Whitefish Bay and Thunder Bay.
The Lake Michigan-Huron open basins away from embayments have modest seiche signals because the wind alignment with the basin geometry is less consistent than on Lake Erie. The Straits of Mackinac do experience bidirectional flow in response to wind, with sustained west wind driving flow from Lake Michigan toward Lake Huron and sustained east wind reversing the direction. See Mackinac.
The basinwide lake level on the homepage is the right starting point. Beyond that, three signals matter for seiche-prone shoreline:
The wind forecast for the next 24 to 48 hours. Sustained wind in the alignment direction of the lake or bay is the trigger for significant set-up. The National Weather Service marine forecast for the specific water body is the relevant source.
The local gauge nearest your property. Most major embayments have multiple NOAA or USACE gauges. The gauge nearest the property is the most useful real-time signal because the basinwide value will not capture the local set-up.
The historical pattern for the season. Fall and early winter (October through December) are the peak seiche-event seasons because the prevailing wind speeds are highest and the atmospheric pressure gradient is most active. Summer seiche events do occur but are less frequent and typically less severe.
For current readings, see the live dashboard. For sub-region-specific seiche behavior, see Saginaw Bay, Western Basin of Lake Erie, Eastern Basin of Lake Erie, and Green Bay. For the regulatory context that determines what property owners can do in response to seiche-driven shoreline change, see Ordinary High Water Mark.