How to Tell Fish from Weeds on Sonar Images
One of the most common sonar mistakes is confusing fish with weeds. Both can appear as marks on the screen, but they behave very differently. By paying attention to shape, consistency, and location, you can quickly tell them apart.
1. Shape: Fish vs Weeds
Fish shapes
Arches, dots, or short lines
Smooth and defined edges
Often separated from the bottom
Weed shapes
Tall, uneven, or fuzzy marks
Thick lines rising from the bottom
No clear arch shape
2. Consistency Over Time
Fish
Appear and disappear
Change shape as they move
Do not stay in one exact spot
Weeds
Stay in the same place
Look the same as the screen scrolls
Create a continuous pattern
If the mark stays solid and unchanged, it is likely weeds.
3. Location on the Screen
Fish
Can be suspended off the bottom
May appear above weeds or structure
Often grouped in schools
Weeds
Always grow from the bottom up
Form a solid layer or wall
Stop at the same depth across the screen
Quick Beginner Tip
Turn your sensitivity down slightly. Fish marks will usually remain visible, while weeds often fade or break up.
Final Thought
Fish move. Weeds do not. Watching how marks change over time is the easiest way to tell the difference on sonar.
