Reading the screen.
A fish-finder is only as good as the person reading it - and at first the screen looks like noise. Once you learn a few shapes, though, it turns into a live map of the water: where the bait is, where the bottom hardens, where fish are holding. Here's how to read it.
A fish shows as an arch, not a fish shape, because the sonar cone hits it as the boat passes over: the return gets closer then further, drawing a rainbow.
On the waterA full, fat arch = a fish that stayed in the cone (often bigger or holding still). Half-arches and dashes are fish passing through the edge of the beam.
Clouds, blobs or a 'pixel storm' of tightly packed dots are schools of baitfish - and gamefish are rarely far away.
On the waterFind the bait and you've found the fridge. Look for arches sitting under, beside or through a bait cloud - that's a feeding zone.
The bold line across the bottom is the return off the lakebed. A thick, bright, wide return means a hard bottom (rock, gravel); a thin, faint one means soft mud or silt.
On the waterFish relate to bottom changes. A hard-to-soft transition, or the base of a drop, concentrates fish more than a flat, featureless bottom.
A fuzzy, horizontal band suspended in open water is often the thermocline - the layer where warm surface water meets cold deep water.
On the waterIn summer, fish frequently stack just above it, where oxygen and temperature are comfortable. Set your lure to run at that depth.
Humps, points, sudden drop-offs (structure) and standing timber, rocks or weed (cover) show as spikes, mounds and fuzzy vertical shapes rising off the bottom.
On the waterStructure and cover are where fish live. Mark the good ones with a waypoint so you can drift or cast back over them.
Traditional 2D sonar draws the arches and history you learn to read first. Down/Side imaging paints a photo-like picture straight down or out to the sides.
On the waterLearn 2D first - it's the fastest way to spot bait, arches and the thermocline. Add imaging later to see exactly what the structure looks like.
Reading the screen is half of finding fish - reading the water itself is the other half. Pair this with reading the water, time it with the best fishing times, and match your depth with the sinker weight guide.
⚠️ A general guide - every sounder, transducer and body of water paints things a little differently, and settings (sensitivity, range, frequency) change what you see. Use this to learn the shapes, then spend time watching your own unit over water you know to calibrate your eye.