Draw the submerged area in the middle of a blank paper. The northern part of the lake or sea must be on the upper side of the paper. Leave some space near the four sides of the paper.
Design the contour lines -- or isobaths -- to depict the depth levels of the submerged area. Use 30-feet or 50-feet isobaths for moderately deep lakes and up to 1,000-feet isobaths for deep parts of oceans. Starting from the edge of the submerged area, you must draw a contour line every time the area becomes 30, 50 or 1,000 feet deeper.
Use different colors to depict each level of depth. To avoid creating a rainbow, which can be confusing, use dark blue for shallow parts, light blue for moderately deep parts and orange for deep parts of the submerged area.
Write down the latitude degree of the submerged area's northern part on the top right and left corners of the paper and the latitude degree of the southern part on the bottom right and left corners. Divide the left and right ends of the paper in latitude degrees: for example, if the top latitude is 45 degrees North and the bottom latitude 40 degrees North, divide the two bars into five equally-sized sections. This way, you create the latitude bars of the bathymetric chart.
Repeat the process to add the longitude bars on the top and bottom ends of the paper. In case the chart is about a small submerged area, such as a small lake, divide the latitude and longitude bars into minutes of an arc, the subdivision of the latitude and longitude degrees. Each degree contains 60 minutes and each minute contains 60 seconds.
Add a legend, explaining the meaning of each color you have used in the bathymetric chart. Also, include a bar showing the distance between two points in miles. This way, you help viewers better understand the size of the submerged area.