The floor of eastern Lake Superior consists of numerous troughs and ridges created during the last glacial period. Among those troughs and ridges is the deepest point in the lake. A multibeam sonar survey of the area determined that the previous measurement of the deepest point in the lake was incorrect. Instead of the lake having a maximum depth of 1,330 feet (405 meters), the lake has a maximum depth of 1,265 feet (386 meters). To the right is a 3-D rendition of a portion of the multibeam data with the lake's deepest point in the center of the image. Below are two images of the entire ~15km by ~5km area covered by the survey. In the left image water depth is color coded. The right image is a top view of a 3-D version of the data. If you click on the image, an animation will start of flying through a 3-D version of the data set (AVI file, 18MB).
Below is a chart of Lake Superior showing the location of the deepest point in the lake. This is NOAA chart 14961. You can look at more NOAA charts and the User's agreement online.