How to Read a Fish Finder (The Right Way)

Video how to identify fish on a fishfinder

Fish finders are the single greatest advantage you can use on the water. Understand how to use them to find bass activity and patterns and you’ll be catching more fish in no time.

How to Read a Fish Finder (The Right Way)

Sidescanning sonar has grown tremendously over the past few years, leading to a nearly endless supply of choices of fish finders.

With brands like Garmin, Lowrance, and Humminbird flush with money, the technology also continues to grow with the competition.

With that, confusion also comes along. When you are trying to figure out what the fish are doing while managing everything else on the boat, the last thing you want is a confusing fish finder.

That’s why understanding a fish finder is a game changer. If done correctly, it will lead to serious results. You will find yourself catching more, and the fish that you do catch will be much bigger.

No serious bass fisherman can expect to compete without one.

Further, they will help you grow as a fisherman since they will teach you about the lakes you are fishing. When you combine sonar with GPS, you can virtually map the bottom topography of any body of water. Developing that understanding will prove to be more valuable than anything else when it comes to catching fish.

Ready to learn more? Let’s dive in! 👇

Properly Reading and Understanding a Fish Finder ✅

You need to understand that your fish finder displays actual fish. Many people doubt their equipment, but fish finders don’t lie. Not only do fish finders display actual fish, but they display them so accurately that researchers are harnessing them to conduct research on bodies of water.

The challenge becomes telling things apart. More advanced fish finders will attempt to do this for you, but with the complexity of variables below the boat and lack of a powerful enough artificial intelligence in fish finders, this is usually inaccurate at best. Therefore, you need to develop your own eye for what fish look like on your fish finder.

If your fish finder displays arches, you know you at least have fish under your boat. Fish taper in mass from one end to another. As the boat passes over them, they return signals that begin weak and then grow strong before weakening again. This results in an arch on the screen. When you are scouting new areas to fish for largemouth bass, this can be a very good sign.

Understanding the size of the arch is essential to determining what the arch actually represents. Looking at the length and thickness of the arch will help you figure out what sort of fish you are looking at, or even if it is a fish at all.

The arch length and color are two crucial features that are instantly recognizable as some sort of fish in the water. From there, you will have to leverage your knowledge as a fisherman to discern what type of fish it is.

Color is also a factor if you have one of the more advanced fish finders. The darker the color, the more dense the thing returning the signal is. This will help you gauge the density of the fish arches. It will also help you determine if the arch is just a big wad of grass that is floating along or if it is an actual fish.

However, just finding arches is only a part of the equation. Having the requisite knowledge to pick out bass from other types of fish is critical. Bass, walleye, catfish, and shad all behave differently and pursue prey in wildly different manners. This results in different patterns being displayed on your fish finder.

For instance, when bass sits on the bottom of the lake, they tend to want their space. This results in dots that are typically congregated near a structure of some sort. However, catfish, carp, and other bottom feeders typically look for depressions. The reason is both are pursuing food in their way. Depressions gather trash, and the structure brings in baitfish.

A note on baitfish, you will often see baitfish in open water as a large cluster of little dots. These large bait balls are easy to identify, and if you see larger, darker arches next to them, you can bet that there are fish feeding on them. However, this does not mean that it is the only place to find baitfish. Often when viewing underwater structures, you will see tons of little dots all around it. This is more often bait fish that feed on the aquatic life growing on the structure.

This is why FISH-ID is viewed as less than accurate. If a fish is swimming along, far away from any sort of cover, then you will likely have a positive identification of a fish from FISH-ID. However, the slightest bit of debris can cause it to misidentify or simply not recognize the fish at all. This is where the operator’s interpretation of the data becomes critical.

Reading Depth and Temperature 💡

There are two primary factors you need to understand with any fish finder. These fundamental factors are depth and water temperature. A mobile vessel such as a high-performance fishing kayak will allow you to reach new fishing areas; seeing what’s under the water is crucial.

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While there are a variety of different ways they’re shown, here’s everything you need to know.

Colors 🌈

What do colors mean on a fish finder? We have already touched on how color denotes density on a fish finder. Generally speaking, the denser something is, the brighter the color is. Understanding density will help you discern hardened structures that can be targeted with soft plastics from other, often muddier, elements that hold little to no fish.

Yet, many fish finders offer different color palettes to choose from. Since there is so much information being transmitted on a fish finder screen, you need to make sure that everything is optimized for efficient, fast reading. Choosing a color palette that will allow you to read it no matter if your sunglasses are on or off, the sun is out, or its not, or if you are sensitive to certain colors over others are all factors that should be considered when selecting a color palette.

You should also not be loyal to any one color palette. Many times, conditions will cause you to have to change your color palette. Exceptionally muddy water or soft bottom lakes will often demand you dial up the sensitivity to pick out the hardened structure from the debris. Certain color palettes will make this much easier to read.

Fish Size 📏

Everyone wants to use their fish finder for spotting trophy bass. Though it may seem impossible to the new user, many people know that sonar has been used by researchers for years to find fish and determine their size. This comes down to paying attention to detail and knowing the fish you are pursuing.

That being said, a fish finder is just that, a fish finder. It is a useful tool, but it can only tell you that there is something below the boat returning sonar waves at a rate that is consistent with a fish. It is up to you to make sense of those returns and take action.

Arches will show the size of the return on the screen. If your fish finder is equipped with FISH-ID, it will likely identify a very strong return with a fish icon. However, it will never tell you what type of fish it is simply because it is nearly impossible to know from an algorithmic standpoint. This is where knowing your target fish and their habits come into play.

Trophy bass don’t typically school or move around in open water. This is because it is mostly inefficient to support their mass. Those fish will want to stay close to a structure that is conducive to catching frequent, easy meals. Finding quality structure is key to finding trophy bass.

Another detail that you should always pay attention to is temperature. There is likely not a fish finder on the market that won’t tell you how hot or cold the water is. It is typically displayed proudly on the screen, no matter what setting you have it on. Water temperature is one of the most important numbers to fish as they set their feeding, spawning, and movement plans based solely on water temperature.

If you see a fish that is outside of a depth, water temperature, and away from the structure that would be common to largemouth bass, it probably isn’t one. Many other fish that get quite large behave totally differently from the ambush-loving largemouth. Always keep this in mind when you are trying to decide what kind of fish are showing up on your fish finder.

Bottom Structure 👇

Knowing how to determine bottom structure is one of the key things you should learn early on when getting used to using a fish finder. Knowing what type of structure you are likely to encounter is one of the many things that will suggest the exact variety of fishing line you will need to use, be that monofilament, braided, or fluorocarbon.

Vegetation and mud are the most confusing things to discern on a fish finder screen. This is because they lack density and clearly defined edges that are able to be seen in detail. However, sunken tree tops, logs, stumps, and rocks will have clear edges that are hard to return a bright color. Telling these from other structures is fairly straightforward.

The key thing to know is that you need to match your boat’s speed with the speed and angle the fish finder is set at. Going too fast with a high-frequency, narrow beam will likely produce a lot of noise and less detail than is usable. However, going slow with the fish finder set to a wide, low-frequency rate will make for clear images, but you will be missing out on the detail that the fish finder is capable of producing.

Reading Different Types of Underwater Structure 🎯

Fish finder technology is continually evolving. The military has a unique interest in developing sonar technology as it helps detect an enemy’s presence in the water. However, as DARPA and the Department of the Navy develop technology that supersedes something it already has, it will sometimes allow for older tech to be released to the public.

One such development was the release of CHIRP sonar in July of 1960. When the Navy allowed the civilian sector to see what CHIRP was capable of, a series of papers were published exploring how it could be used and improved.

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Today, CHIRP sonar has changed the way marine biologists identify marine sediment. Biologists, geologists, and other interested parties regularly used high-end CHIRP sonars to explore waters that would otherwise be completely inaccessible. However, it wasn’t long before the word was out, and the recreational fish finder market began to explode.

For years, the common man’s fish finder could tell that there was something on the bottom, but it was very difficult to tell what it was. Modern fish finders have changed this dynamic drastically. Today we can tell what vegetation, muddy bottoms, depressions, points, and underwater structures with relative ease.

Vegetation 🌿

Vegetation is one the most confusing things to read on a fish finder, but one of the most important. This is especially true if you are fishing with bass jigs and need to be precise about where your lure is placed.

Baitfish and vegetation often look very similar since they are assembled similarly and have comparable densities. Therefore, their color and distribution can often result in confusion between the two.

Vegetation is most easily identified by where it is relative to the bottom. Typically, vegetation will always be attached to the bottom. Therefore, when you see a large distribution of dots that seems to ascend from the bottom of the lake, you can guess it is likely some sort of vegetation.

Muddy Bottoms 🐾

Muddy bottoms are also a crucial part of bottom terrain that is advantageous to identify when fishing. One of the most crucial things in any sort of fishing is to figure out what the fish are feeding on. Once you understand the common diet of largemouth bass, then you will know that a muddy bottom is not something you want to pursue.

Muddy bottoms are identified by the color the fish finder returns. Depending on your individual color palette, they could look slightly different from unit to unit. However, the main thing you need to pay attention to is the density of the bottom.

If your unit returns a color that indicates a dense bottom, you can bet there is gravel or rock down there. However, if weaker colors are returned, you know the bottom is muddy.

Depressions 🗺

Another key terrain feature you will want to look for is depression. Depressions are simply low points on the bottom of the lake that gather trash that the current pushes along. This can become a major point of interest for fish, depending on the type. Downed tree tops that collect in depressions will bring in the bass, but bottom feeders also will find them since that is where most of the biomass ends up.

Depressions are easy to locate on a fish finder. As you troll along, pay attention to the depth that the boat is at. When you see a sudden drop in depth, zoom out to get a bigger picture.

This will allow you to chart the size of the depression and make sure it is not a drop-off. As the depth comes back up, mark it and turn the boat around. Then go back over the depression and mark the other side.

Points 💡

Every bass fisherman knows and loves points. Points provide fish with multiple escape routes if danger comes, are often choke points for bait fish that can be food, and provide quick and easy access to all depths of water. If you aren’t fishing over underwater points, you are likely missing the fish of a lifetime every time you motor on by.

Yet how do you find a point on a fish finder? Luckily, it is incredibly easy. A point is a terrain feature that jets out into the water, making an arrowhead shape. The point can either be above or below water. Finding points of terrain features below water is where your fish finder really pays for itself.

Look for areas that have rapid changes in depth. There will be a generally shallower area that gives way to the depths. Somewhere in that shallower area, there is likely to be an arrowhead-shaped structure that sticks out.

Run your boat over it, bisecting the long axis of the point. If using a lighter boat such as a kayak, use a trolling motor optimized for kayaks to quietly navigate over the area, ensuring you’re not spooking any fish. Each time you notice a depth drop-off, mark it. After a few passes, you will have a good understanding of where the point is and how best to leverage the tools in your tackle box to fish it.

Hidden Fish and Beam Width

It is easy to find fish when they are just sitting on the bottom, in a depression, or swimming in open water. However, largemouth bass live in structures that really come in all shapes and sizes. This puts the fisherman in a conundrum. You want to fish that structure, but you also don’t want to waste a lot of time on a structure that hasn’t attracted any fish.

The answer to this is beam width. While fish will hide in stumps, trees, and other structures that can be detected by a wide beam angle, they can’t be picked out. You will need a higher frequency, more narrow beam to be able to detect the fish that are held up in the cover.

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Think about the beams like a flashlight. You will use a flood light if you want to see a lot. It doesn’t show the detail of anything, but it will let you see enough to know where everything is. However, in trying to find hidden fish, you will need a high-intensity spotlight to see the differences between the structure and the fish.

You should troll, cruise, and scout using a low-frequency, wide-beam setting on your fish finder. Once you have located some structure, mark it and then turn around with a high frequency, narrow beam setting enabled. Go slower on the second pass, and you will be able to pick apart the fish from the structure with relative ease.

Reading Chirp Sonar

One thing to note about CHIRP sonar is that it is incredibly powerful. CHIRP is powerful enough to even read the grain size of sediment on the bottom of the ocean. This is very helpful in finding transition zones in the bottom sentiment. These transition zones often bring in a variety of different types of fish, including bass.

While CHIRP is nothing more than an enhanced way to read sonar returns, this means that there is nothing different that you have to learn or do, just that your fish finder will provide you with a more powerful readout than a non-CHIRP fish finder. However, always defer to the CHIRP-enabled fish finder since it will give you a clear picture of the bottom, which is helpful when a rainy day completely disrupts your surface presentations.


There is no magic bullet when fishing. Even if you get a top-of-the-line fish finder, you still have to know how to fish. In a two-day study of crappie fishermen, researchers found that using a state-of-the-art fish finder had no real impact on the angler’s ability to catch fish. This means that if you control the environment, a good fisherman catches more fish with a fish finder, but a bad fisherman still catches no fish.

The lesson to take away is that a fish finder is just a tool that helps you be more efficient and effective when fishing. It will not be the answer to all your fishing challenges, but if you know how to properly employ it, it can be a great asset.

Understanding a Fish Finder: FAQs

What do bass look like on side imaging?

Bass generally appear as a dot on side imaging. Due to their behavior and preferences for being somewhat distant from other fish, it is often easy to find them sitting on the bottom or around cover. This method of identifying fish can be very effective. Side scan imaging is used widely to determine fish species on artificial reefs.

What’s the best frequency for a fish finder?

The best frequency for a fish finder is around 125 kHz. Fish finders generally range from 50 to 200 kHz. The lower end of the spectrum is better for wide-angle searches, but the higher end is good for high-fidelity imaging of certain areas or targets. Using a fish finder that straddles those two extremes gives you the most versatile tool available on the market today.

Can you see a lure on side imaging?

You can most definitely see a lure when you are using live sonar, but side imaging does not have the high level of fidelity required to give that level of detail fast enough to show your lure. While they are much more expensive, live sonar can be a highly beneficial upgrade to catch fish when they would otherwise be inaccessible.

How do you spot fish on sonar?

You spot fish on sonar by looking for arches or lines on the screen that are above the bottom of the lake. Depending on your setting, speed, and location of your transducer, fish detection can look much different from setup to setup. However, generally, a moving boat will show fish as arches, and a boat that is still will show them as lines.

Do you have to be moving for a fish finder to work?

You do not have to be moving for a fish finder to work. However, it is vital that you have your fish finder settings adjusted to properly compensate for the movement of your boat. If you anticipate moving at a fairly brisk pace, you want to set your fish finder up so that it also scans more frequently. However, if you have your transducer mounted to a trolling motor and don’t anticipate moving very quickly, then you will want to slow the scroll rate down to match the speed of your boat.

What do fish look like on a fish finder?

Fish look like arches on fish finders, generally speaking. However, depending on the setup and speed of the boat, fish can have a slight variance in how they look. As the boat moves over the fish, the fish is hit multiple times by sonar waves. Since they generally taper in size since the tips of tails and noses don’t have as much mass as the middle of a fish’s body, the first returns show a smaller creature. The returns increase the size of the creature it is encountering as it works its way to the middle point of the fish. After this, the returns show the fish decreasing in size. The graphic result of this is an arch.

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Ethan Smith is a seasoned marine veteran, professional blogger, witty and edgy writer, and an avid hunter. He spent a great deal of his childhood years around the Apache-Sitgreaves National Forest in Arizona. Watching active hunters practise their craft initiated him into the world of hunting and rubrics of outdoor life. He also honed his writing skills by sharing his outdoor experiences with fellow schoolmates through their high school’s magazine. Further along the way, the US Marine Corps got wind of his excellent combination of skills and sought to put them into good use by employing him as a combat correspondent. He now shares his income from this prestigious job with his wife and one kid. Read more >>