International Great Lakes Datum

The International Great Lakes Datum (IGLD) is a common reference system used to measure water level heights throughout the Great Lakes, their connecting waterways, and the St. Lawrence River System. A common system is needed for marine navigation, water level regulation, water management, surveying, mapping, and shoreline use planning. Established in 1955, the IGLD is a binational effort between the United States and Canada that ensures cohesive water management in eight states and three provinces. The IGLD is managed by a binational group of federal scientists known as the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data and its Vertical-Control Water-Levels SubCommittee (SC).


The 2020 Update: A New IGLD Is Coming!

To account for movements of the Earth’s crust and accurately measure water levels, the IGLD needs to be updated approximately every 25-30 years. CO-OPS and its partners currently utilize IGLD 1985. This existing IGLD will be revised over the next several years and replaced by IGLD (2020). As part of the revision, the SC will also evaluate and potentially revise the Low Water Datum (LWD). IGLD (2020) will align with the National Geodetic Survey’s new geoid-based North American-Pacific Geopotential Datum. The new IGLD is scheduled for tentative release in 2025.

A NOAA Sentinel station, which is a hardened water level observation station able to survive severe meteorological events.
In the Great Lakes, glacial isostatic adjustment (e.g., movement of the earth’s crust) is a primary contributing factor to changes in the International Great Lakes Datum and a significant reason behind why the Datum must be periodically updated. Source: Mainville and Craymer, 2005.
Contact Us

If you have general questions about the International Great Lakes Datum or the 2020 update, please email us at tide.predictions@noaa.gov.

For media-related inquiries, please contact nos.co-ops.commsteam@noaa.gov.