Bathymetry is the measurement of the depth of water in oceans, seas, lakes, or ponds. Bathymetric maps look a lot like topographic maps, which use lines to show the shape and elevation of land features. On topographic maps, the lines connect points of equal elevation. On bathymetric maps, they connect points of equal depth. 

Bathymetry has been used in many forms for hundreds of years. In ancient times, scientists would conduct bathymetric measurements by throwing a heavy rope of the side of a ship and recording the length of rope it took to each the seafloor. These were highly inaccurate measurements and needed thousands of measurements to make a map. 

Today, sonar or echo sounders are used to make bathymetric measurements. These devices sends out a sound pulse from a ship's hull, or bottom, to the bottom of the water body. The sound wave bounces back to the ship. The time it takes for the pulse to leave and return to the ship determines the topography of the seafloor. The longer it takes, the deeper the water. 

Sonar based mapping technology is extremely useful for lake management.

These management tactics are as follows:

• Sonar-based mapping technology has the capability of developing aquatic vegetation maps of a lake or pond. These maps can be incredibly helpful in developing plans, budgeting, and permitting. 
• Mapping can help identify opportunities to enhance your fishery. Assessing depth can help identify fish habitat needs within the water body. 
• Lake mapping can be useful in identifying the water volume of a water body.  This knowledge can be used for historical data and also resource management for municipal water resources. 
• Mapping of sediments on a water body can help identify effective strategies for dredging, sediment phosphorus management, or tracking sedimentation accumulation over time due to erosion. 

While there are many ways to manage a waterbody, bathymetry can be a management tactic to add to our toolboxes for lake management. Having knowledge of what is going on both at the top and bottom of a water body can inform and improve overall management.