How to Read Fish Finder Sonar

Modern fish finders allow anglers to see fish, structure, and vegetation beneath the boat. However, many anglers struggle to interpret what they see on their screen. This guide explains how to identify fish, structure, weeds, and bait using sonar.

Sonar traditional 2D

Fish appear as arches or partial arches.

Down imaging

Fish appear as bright dots or small streaks.

Garmin 2D sonar images of baitfish and bass
Garmin 2D sonar images of baitfish and bass
Garmin down imaging of bass in lake . shows as small dots
Garmin down imaging of bass in lake . shows as small dots
Garmin side imaging showing bass and shadow
Garmin side imaging showing bass and shadow
Side imaging

Fish appear as bright spots with a dark shadow behind them. The shadow on side imaging helps determine how far the fish is off the bottom.

Fish

Fish vs Structure vs Weeds Section

Walleye on Side Imaging
  • Bright, elongated shape slightly above the bottom.

  • Often accompanied by a dark shadow behind it, which helps indicate how far it is from the bottom.

Various Structures

Structures on Side Imaging Sonar

  • Hard objects like rocks, brush piles, or submerged trees reflect strong signals show up bright on screen.

Structures on Down Imaging Sonar

  • Can see fine details of objects like branches, rocks, and drop-offs.

walleye sonar images on side view on Garmin sonar in lake
walleye sonar images on side view on Garmin sonar in lake
Garmin sonar images of branches and rocks on side view and down view
Garmin sonar images of branches and rocks on side view and down view
garmin sonar images of vegetation on 2D and side view
garmin sonar images of vegetation on 2D and side view
Weeds

Weeds on 2D Sonar

  • Appear as fuzzy or cloudy shapes rising from the bottom. Look like vertical streaks or irregular masses.

Weeds on Side Imaging Sonar

  • Show up as dense, textured patches along the bottom. Form long lines or clusters along the edges of open water.

Other images.....

Bass along weed lines

Bass holding just outside a weed line visible on down imaging sonar.

Bass often position along weed edges where they can ambush baitfish moving along the vegetation line.

bass hiden in weeds in lake. sonar image of down view
bass hiden in weeds in lake. sonar image of down view
garmin 2D sonar image of baitfish in lake
garmin 2D sonar image of baitfish in lake
Baitfish

Large baitfish school detected on sonar.

Bait schools appear as dense cloud-like clusters on sonar.

side imaging of rocks and bolders on Garmin sonar
side imaging of rocks and bolders on Garmin sonar
Rocks / Bolders

Rock pile structure visible on side imaging sonar.

Hard structures such as rocks return strong sonar signals and appear bright on the screen.

lake trout on Garmin sonar in lake 2D image
lake trout on Garmin sonar in lake 2D image

Suspended trout visible above deep water on sonar.

Lake trout suspended

For more sonar images and information, visit

Sonar settings for fish

Sonar images: fish and structure

body of water