• Chart depths references will change.
• The Low Water Datum (LWD) — which is the accepted base elevation for the Great Lakes and adjoining major river systems, and is the basis for the water depths listed on navigational charts — will also change from IGLD (1985) to IGLD (2020).
• The LWD also sets authorized depths for navigational improvement projects such as harbor dredging, which may affect dredging depths and cost and volume of dredge material.