How Does a Fish Finder Work? The Scoop on This Fishing Companion

It sure would be handy if you could see down in the murky water so you could reel in the biggest catch of the day. Luckily, you brought along a fish finder to help, but how does a fish finder work?



Humminbird 410210-1 HELIX 5 CHIRP GPS G2 Fish finder

Image from Amazon

A fish finder works by using a sound navigation and ranging (SONAR) system to peer down into the depths. You’re utilizing an echo! The soundwaves produced by the fish finder bounce off objects underneath the waves to bring you a picture of what’s there — including fish. It also tells you how deep the object is.

But there are more solid things under the water besides fish, so how does a fish finder work to locate what you want to catch?


The fish finder attached to your boat produces a small soundwave, which grows as it travels through the water. When it hits an object, it bounces off of that object and travels back to the fish finder.

So, the fish finder uses the time it takes for the soundwave to travel back to determine how deep the object is and exactly where it is underneath the surface. That helps you determine where to cast your line.

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SONAR waves are going to pick up everything in the water, including your fishing line, so how can you tell you’re looking at fish?

While it might be nice to see a fish shape down in the water, that’s not what the soundwave is going to bounce back. You’ll get to know what’s what by simply using your fish finder.

The fish are moving, of course, and the fish finder is constantly sending down soundwaves, so you won’t see fish-shaped blips on the screen. Instead, you’ll likely see trails.

Notice how you can see the fishing lines bobbing up and down? Then you can see the fish as they swim up to the lines and back down again. You can also see the trail of the fish who are hanging down below.


When using your fish finder, you’ll get to know what the images are that are coming back to your screen. If you have a color screen, the different colors will also give you a clue as to what you’re looking at.

Humminbird 410210-1 HELIX 5 CHIRP GPS G2 Fish finder

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Image from Amazon

Remember, the fish finder works by sending a soundwave down into the water. Smaller objects will have a smaller surface area to bounce the soundwave and will show a smaller picture on the screen. They will also typically be a consistent color or shade.

Usually, solid objects will be the darkest — think rocks. Fish will be lighter in color or shade and will be smaller. They’ll also likely be moving in the water.


Deeper Chirp Smart Sonar – Castable, Portable Fish Finder...

Image from Amazon

If the answer to the question “How does a fish finder work?” sounds familiar — it should. After all, there are natural fish finders who’ve been using this technology since the beginning of their existence.


Deeper Chirp Smart Sonar – Castable, Portable Fish Finder...

Marine animals, like whales and dolphins, use biosonar to find their prey and they are the best fish finders. They also use it to locate their families and familiarize themselves with their environment under the ocean.

Using their own soundwaves, they can tell not only the location of an object, but also where it is, its shape, and whether it’s coming toward them or moving away.

So, when you’re thinking, “How does a fish finder work?” and you’re happy about how easy it is to find fish, thank the marine animals for their technology.

And you might be interested to know that it’s not just whales and dolphins who use this tech. Many fish and invertebrates use sound for food and other reasons like warding off predators.


red fish

image by pixabay

Now that you know “How does a fish finder work?” you can use that knowledge to understand what you see on your fish finder screen. And the more you use your device, the easier you’ll be able to read it, so you’ll know exactly where and when to cast your line.

One thing to note: Read the instructions that come with your fish finder. In order to see what you want to see, you need to know the proper settings.

You can change the depth in which you’re looking as well as the angle you’re sending the SONAR wave. Plus, most allow you to use filters to better understand the environment under the water as you fish. So, know your fish finder before you head out.

How does a fish finder work to help you with your fishing adventures? Tell us your fish tales in the comments!

Featured Image by Florida Fish and Wildlife from Flickr

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