This map shows the bathymetry, or depths, of Lake Michigan. The deepest parts, reaching 280 meters (923 feet), are shaded dark blue. As glaciers retreated from the region some 10,000 years ago, these deep parts formed a smaller lake, known now as Lake Chippewa.
To make this map, researchers compiled data from more than 120 years of soundings (depth measurements). This work was done by the NOAA National Ocean Service and its predecessor agency for Great Lakes surveying, the U.S. Army Corps of Engineers.
Over 600,000 bathymetric soundings were employed in compiling this map. About 60 percent of these were already in digital form, while the remainder were digitized for the effort. This map revealed lake bottom features more accurately than ever before and showed some features for the first time. One of those is the Mackinac Channel, which can be seen in the northern part of the lake. This was a river that drained Lake Chippewa.
NOAA is engaged in a program to compile Great Lakes bathymetric data and make them readily available to the public, especially to the communities concerned with Great Lakes science, pollution, coastal erosion, response to climate changes, threats to lake ecosystems, and health of the fishing industry.