How to Use a Fish Finder: A Beginner's Guide to Reading Sonar

A fish finder is the single biggest upgrade most anglers can make. Instead of guessing, you see depth, bottom structure, weeds, bait and fish in real time. The screen can look confusing at first, so here is a plain-English guide to reading sonar and putting it to work.

How a fish finder works

The transducer sends a pulse of sound down through the water. When that sound hits something (the bottom, a weed bed, a school of baitfish or a single fish) it bounces back. The unit measures how long the echo took to return and draws it on the screen. The newest return appears on the right, and the picture scrolls to the left as time passes.

Reading the screen

• The bottom is the thick, bright band at the bottom of the screen. A thin line means soft mud; a thick, bright line usually means hard rock or gravel.
• Fish arches appear when a fish passes through the cone. A full arch means the fish moved all the way through the beam. Half arches and short lines are still fish.
• Bait balls show as dense clouds or blobs, often in the middle of the water column. Predators are rarely far away.
• Weeds and brush rise up from the bottom like grass or trees. These are classic ambush spots for bass and pike.
• Fish icons are the unit's best guess. Many anglers turn fish ID off once they learn to read raw arches.

Five settings worth learning

1. Depth range: set it a little deeper than the water so the bottom sits near the bottom of the screen.
2. Sensitivity: turn it up until you see some clutter, then back off slightly.
3. Fish alarm: great for shore and ice fishing; it beeps when fish move under the sensor.
4. Depth alarm: warns you before you drift into shallow water.
5. Frequency: higher frequencies show more detail in shallow water; lower frequencies reach deeper.

Turning sonar into bites

Use the fish finder to scout first and fish second. Idle or drift over drop-offs, points and weed edges until you mark bait or fish, then back off and cast to the spot. On the ice, watch your lure on the screen and see how fish react to different jigging cadences.

Which fish finder should you get?

Shore and kayak anglers love castable and wireless fish finders because there is nothing to mount. Boat anglers can use a portable unit with a wired transducer. Not sure which style fits? Read our guide to castable vs wireless vs transducer fish finders, or use the Tackle Finder for a personal recommendation.