The method for determining the depth of a lake depends on the resources available to the person making the calculation. Furthermore, there are multiple types of depth measurements. The mean depth of the lake is the volume divided by the surface area. You can use a fish finder or a rope with a weight to determine the depth of a lake. However, these technologies are only valuable for finding the depth at a specific place. To find the deepest point, you must take the measurements in several locations.

### Determine Lake Depth with a Sonar

Mount a fish finder sonar on a boat.

Launch the boat.

Turn on the sonar.

Move the boat across the lake while watching the depth number. Note where the deepest points are along the way.

Spiral in around the deepest points to find which is the deepest.

### Determine Lake Depth with a Rope and Weight

Tie the rope to the weight.

Bring the boat to the middle of the lake.

Lower the weight into the water slowly. When it touches the bottom, mark the rope and pull the weight back.

Lower the weight in several nearby locations. If the deepest mark is under water, mark the new deepest point. Continue until satisfied with the accuracy of the depth point.

Move to land and measure the rope with a tape measure.

### Find Lake Depth Information on the World Lake Database

Launch a web browser.

Search the World Lake Database for the lake whose depth you are measuring.

Write down the deepest point and the mean lake depth.