Datum Updates
Tide and water level datums are standard elevations used to reference water level heights and depths. Each type of datum represents a unique phase or behavior of the water along the coast or in the Great Lakes. CO-OPS and its partners are currently in the midst of two large-scale datum updates for the National Tidal Datum Epoch (NTDE) and the International Great Lakes Datum (IGLD).
To obtain datums for a specific location, please visit the CO-OPS Datums Station Selection web pages.
National Tidal Datum Epoch
The NTDE is a specific 19-year reference period over which water level observations are taken to determine Mean Sea Level and other tidal datums (e.g., Mean Lower Low Water). The NTDE has historically been updated every 20-25 years.
International Great Lakes Datum
The 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. The IGLD is updated every 25-30 years.
