Things You'll Need:
- GPS system
- Sonar system
- On board computer
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Step 1
Use a GPS system to determine a transect line across the lake. Run the transects on longitude and latitude lines. Electronic echo sounders are used along the transect line to gauge the depth. For lakes smaller than 2,000 acres, you can bypass the GPS and just line up your sight from one landmark to another across the lake and follow that as you line of sight transect line.
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Step 2
Go to the beginning of the transect line on the lake in your boat. Turn the sonar unit on and start idling the boat, moving along the transect line, guided by the GPS. You might want to have a partner with you to drive the boat and follow the GPS while you use the sonar.
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Step 3
Watch the screen. The line of dashes at the top indicates the water's surface. In the upper left corner of the screen the current water depth will be displayed. It's as easy as that. The computer does all the work for you, short of driving the boat. If the unit is in an automatic mode, the depth will change as the boat moves.
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Step 4
Interpret what you see on the screen. Look for gray near the bottom. It will be either a thin line or a line of gray that is much wider. If the sonar signal bumps off of brush or trees, a large gray area will appear. This will give you an idea of what the bottom of that part of the lake is composed of. Sand and mud also absorb the signal and scatter it so the sonar echo is not as strong and will show up as a thin line while a wide line will mean the signal has echoed off of a hard bottom like rock or shale.
