The Great Lakes record water levels are the anchor points that shape every property-owner conversation about shoreline planning, and Chris Izworski tracks them because the records define the regulatory baseline (OHWM elevations are set against historical reference periods), the engineering baseline (shoreline protection is designed against expected maximum levels), and the policy baseline (federal and state shoreline programs reference the high and low cycles when setting funding, permitting, and disaster declarations). The U.S. Army Corps of Engineers and the Canadian Hydrographic Service maintain the official record back to 1918, with shorter records for many specific gauges.
Period of record: 1918 to present for the coordinated lake-wide average; longer for some individual gauges.
Reference highs: 1986 cycle on the upper lakes, 2019 to 2020 record cycle on the upper lakes, 1973 and 1986 cycles on Lake Ontario, 2017 record on Lake Ontario.
Reference lows: 1925 to 1926 (Lake Superior), 1934 (Lake Erie), 1964 (Lake Michigan-Huron), 2013 (modern low on the upper lakes), 1934 (Lake Ontario).
Datum reference: International Great Lakes Datum 1985 (IGLD85), the standard reference plane for all Great Lakes elevations.
Data sources: NOAA Great Lakes Environmental Research Laboratory, U.S. Army Corps of Engineers Detroit District, Environment and Climate Change Canada.
Lake Superior (datum 601.10 feet IGLD85) reached its modern record monthly high of approximately 602.85 feet in October 2019, narrowly exceeding the prior high cycles of 1985 and the late 1990s. The modern record low was the prolonged 1925 to 1926 period, with monthly values below 600 feet for an extended stretch. The 2007 cycle was the most prominent recent low. Superior's overall range is the narrowest of the Great Lakes because of the lake's size and the IJC regulation framework that smooths outflow.
Lake Michigan-Huron (datum 577.50 feet IGLD85, shared between the two lakes hydraulically) reached its record monthly high of approximately 581.70 feet in July 2020, surpassing the prior 1986 cycle high. The modern record low was the January 2013 monthly value of 576.02 feet, exceeding the prior 1964 low. The Michigan-Huron range from 2013 to 2020 (roughly 5.7 feet) is one of the most dramatic short-period swings in the modern record, and the property-owner experience through that swing shaped substantial policy debate around the OHWM, shoreline protection permitting, and regulatory adaptation.
Lake Erie (datum 569.20 feet IGLD85) reached its record monthly high during the 2019 to 2020 cycle, with peak values near 574 feet. The record low was the 1934 cycle. Erie's range over the modern record is roughly 6 feet from peak high to peak low. The lake's shallow geometry means that even modest changes in the basinwide level interact strongly with the seiche and storm-surge dynamics that affect property owners on a day-to-day basis. See Seiche.
Lake Ontario (datum 243.30 feet IGLD85) reached its record monthly high in May and June 2017, with another high in the 2019 cycle. The 2017 peak was the highest single monthly value in the period of record. The Lake Ontario regulation framework (Plan 2014 currently, Plan 1958-D previously) actively manages outflow to balance multiple competing interests, and the policy debate around the regulation plan is the dominant property-owner conversation along the Lake Ontario shoreline.
The records are not predictions. They are the historical baseline against which current conditions and future planning are evaluated. Three implications matter most for property-owner planning.
The OHWM is anchored to historical highs. The Michigan OHWM on Lake Michigan-Huron at 581.5 feet IGLD85 is set just below the 2020 record. The OHWM on Lake Superior at 603.0 is set near the 2019 record. The OHWM is the regulatory line for submerged-lands ownership and shoreline-alteration permitting, which means that the historical record literally defines the legal landscape for shoreline property. See Ordinary High Water Mark.
Shoreline-protection design is anchored to expected high water plus storm surge. Engineers and contractors designing shoreline-protection structures typically use the 100-year return level (the level expected to be exceeded with 1 percent probability in any given year) plus a storm-surge or seiche allowance plus a freeboard margin. The 2019 to 2020 cycle exceeded the prior 100-year estimates derived from pre-2019 data, which has prompted re-estimation of return-level expectations across the basin.
The historical range shapes the policy and insurance conversation. Federal flood-insurance programs, state shoreline-protection grants, and municipal coastal-hazard regulations all reference historical lake-level cycles when setting program parameters. The combination of the 2013 low and the 2019 to 2020 high in a single decade has accelerated the policy conversation about how to plan for an apparently wider range of variability than the prior decades suggested.
The 108-year coordinated record (1918 to present) captures most of the modern instrumental period but is not long enough to fully characterize the natural variability of the Great Lakes basin. Tree-ring reconstructions, sediment-core analysis, and shoreline-geology studies indicate that the lakes have experienced both higher highs and lower lows in the recent geological past than have been observed during the instrumental record. The Lake Algonquin and Lake Nipissing high stands during the post-glacial period left shoreline features at elevations well above any modern record, and the deep low stands during cooler periods left features well below modern lows.
For modern property-owner planning, the instrumental record is the relevant baseline, but the longer geological context is a useful reminder that the lakes are dynamic systems with substantial variability on multiple timescales. The trend over the past several decades has been toward greater amplitude in the lake-level cycle, with more dramatic swings between highs and lows over shorter periods. Whether this trend continues, reverses, or stabilizes is one of the more actively debated questions in the basin's water-resource science community.
For current readings, see the live dashboard. For the regulatory context that ties historical records to property-owner planning, see Ordinary High Water Mark and Shoreline Erosion. For lake-by-lake current conditions, see Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario.