Reading a River Depth Finder

Reading a River Depth Finder: What Kenai River Guides Actually Use

A depth finder (sonar/fish finder) on a Kenai River drift boat or jet sled is a navigation and structure tool first, a fish locator second. Understanding what the screen is showing — and what it isn't — is what separates productive use from expensive decoration.

Basic Screen Interpretation

• The bottom line: The solid return at the base of the screen. On the Kenai, this should be a relatively sharp, hard line (cobble and rock). A soft, fuzzy bottom line indicates silt or sand — not typical Kenai substrate, but found in some slower side channels.
• Depth reading: Displayed in feet or meters. On the lower Kenai (Soldotna area), productive King holes run 15–35 feet. Set your display range to 40 feet to keep the full water column visible.
• Fish arcs: Individual fish return as arches on the traditional 2D display — the transducer passes over the fish and creates the arc shape. Strong arches = large fish. Partial arches = fish at the edge of the cone angle.

What the Kenai's Bottom Structure Looks Like

• Hard, flat bottom: Fast water, likely swept clean — fish may transit here but won't hold. Keep moving.
• Irregular bottom with depth variation: This is what you want. Pockets, shelves, and holes behind boulders show as dips and rises in the bottom line. These are holding areas.
• Boulder fields: Show as hard, irregular bottom return with scattered high-amplitude returns. Fish hold in the downstream shadow of large boulders — the depth finder shows where those boulders are.
• Drop-offs: Abrupt depth changes (5 to 20 feet over 10 feet of drift) indicate current breaks — prime salmon holding. The transition between fast and slow water is where Kings stack.

Settings for Kenai River Use

• Sensitivity: Start at 75–80%. High enough to show fish but not so high that bubbles and turbulence create false returns in fast water.
• Frequency: 200 kHz for shallow water (under 30 feet) — better resolution, narrower cone. Use on the Kenai for detail work in holes.
• Speed: When drifting at river speed, scroll speed on traditional 2D should be set to match. If drifting fast, increase scroll speed to see a realistic picture of what's below.
• Zoom: Use bottom zoom to expand the bottom 10 feet of the water column — this is where salmon hold and where you want detail.

What Depth Finders Cannot Tell You

A depth finder shows you structure and position of fish. It does not tell you species, whether the fish are actively biting, or water clarity. Guides use depth finders to navigate to productive structure — then rely on local knowledge, observation, and technique to actually catch fish. It's a tool, not an oracle.