How to Read a Fish Finder


Fish finders featuring side imaging technology

Using a fish finder to view underwater structures and locate fish is a great way to make the most of your day on the water. However, understanding how a fish finder works and reading a fish finder can be a little overwhelming, especially for beginner anglers. Whether you’re looking to buy a new fish finder or needing some help understanding how to use your fish finder, our expert anglers walk you through how a fish finder works and how to read fish finder sonar.

How Does a Fish Finder Work?

When looking at a fish finder you will notice two main parts—the fish finder display and the transducer. The fish finder display is placed in your boat, while the transducer is in the water to emit sonar. Sonar stands for Sound Navigation and Ranging and is a way to measure the depth of an object in water such as a fish or the bottom of a lake. 

In order to receive information about what’s below the water, the transducer sends sonar pulses throughout the water. Once the sonar pulses hit an object, the estimated size and depth is sent back to the transducer. Acting as a small computer, the fish finder receives the transducer’s sonar and displays this information digitally for the angler to interpret.

How to Read a Fish Finder

In order to use your fish finder properly, you need to know how to read the fish finder screen and data that appears. There are five popular types of sonar technologies that influence the way the fish, structures, and bottom appear on the fish finder display screen. It’s important to note that depending on your fish finder, you could have access to a combination of these different sonars.

2D Sonar & CHIRP Sonar

Fish Finder featuring 2D sonar

2D sonar is a great way to scan for schools of fish because the images don't come in as clear as other sonar options. Schools of baitfish, weeds, and larger structures appear as colorful blobs, while arches, color marks, or clouds represent game fish or baitfish. 

2D sonar has greatly improved with the option of CHIRP sonar. CHIRP sonar was developed to excel in deep water that’s greater than 25 feet. The difference between traditional 2D sonar and CHIRP sonar is the number and range of frequencies emitted from the transducer. Compared to traditional 2D sonar, these images come back clearer and more well-defined so you’re able to easily distinguish between bait and game fish as well as structure and vegetation. 

Down Imaging Sonar

Fish Finder featuring down imaging sonar

If you're fishing in or around cover, using down imaging sonar comes in handy. Just as the name describes, down imaging sonar allows anglers to see directly under their boat. Although down imaging provides anglers with a very small picture of the water, these sonar images come back more picture-like rather than traditional 2D sonar, making it easier to identify game fish thanks to the bright coloring and dark shadows.

Side Imaging Sonar

Image of a side scanning sonar

For those who spend more time fishing in shallow waters or looking to cover large expanses of water no matter the depth, you may be interested in using side imaging sonar. With side imaging sonar, you’re able to see a great range on either side of your boat. Unlike other sonar technologies, side imaging sonar is read top to bottom with your history moving towards the bottom. Similar to down imaging, side imaging sends picture-like sonar images to your display so you can clearly identify objects like fish, rocks, and other structures as well as locate depth based on shadows.

360 Imaging Sonar

The 360 imaging sonar is an exclusive to Humminbird that constantly updates while moving or sitting still to provide views in every direction around your boat as well as below. The sonar images received are similar to both down and side imaging so you’re able to clearly distinguish the structures below the water. With this type of sonar, you won’t risk spooking the fish and you’ll have more accurate casts.

Live Scanning Sonar

Fish finder with live scanning sonar

A major breakthrough in sonar technology is live scanning sonar. With live scanning sonar, you’re able to see what’s happening in real time below and around your boat. The sonar images received on your fish finder allow you to clearly view details of both fish and structures. With this real-time feedback, anglers can change their strategy to encourage a strike.

Fish Finders & GPS

When looking for a new fish finder, you may be tempted to skip the GPS technology feature because of the cost. Although a fish finder with GPS does cost more, many beginner anglers may feel more comfortable having this feature when on an unfamiliar lake or river. With a GPS fish finder, you can quickly find a desired location along with marking spots in which you would like to return. Plus, you can combine your GPS with charts or maps, like Navionics®, so you’re able to see structure or depth changes of the lake.

Understanding the basics of how a fish finder works and how to read your fish finder sonar will make you more successful on the water. Each year fish finding technologies are constantly improving to provide anglers with clearer, more detailed information; however, the basics of understanding how to read these different sonar technologies remain the same. If you have additional questions about fish finders, contact one of our fishing experts at your local SCHEELS today!

Article By: SCHEELS