No, you cannot see fish with thermal imaging. Thermal cameras detect infrared radiation emitted by surfaces, and water absorbs that radiation almost completely within a fraction of a millimeter. A fish swimming even a few inches below the surface is entirely invisible to any thermal camera, no matter how advanced.
That said, the answer gets more interesting when you understand exactly why this limitation exists and the clever workarounds that scientists and anglers have found.
Why Water Blocks Thermal Imaging
Thermal cameras work by detecting long-wave infrared radiation, the heat energy that every object naturally emits. The problem is that water is essentially opaque to this type of radiation. Infrared waves penetrate water to a depth of only about 4 to 80 micrometers, depending on the wavelength. To put that in perspective, 80 micrometers is thinner than a sheet of paper. Everything a thermal camera “sees” when pointed at a lake or river is the temperature of that ultra-thin skin on the water’s surface.
This isn’t a limitation of camera quality or technology. It’s basic physics. Even military-grade thermal systems costing hundreds of thousands of dollars face the same wall. The water itself acts as a near-perfect thermal blanket, hiding everything beneath it. A fish could be an inch below the surface and it would be completely invisible.
What You Actually See on a Thermal Screen
When you point a thermal camera at water, you see the surface temperature of the water itself, along with reflected thermal radiation from the sky and surroundings. Water has an emissivity of about 0.98, meaning it radiates nearly all of its thermal energy like a near-perfect blackbody. The remaining 2% or so is reflected infrared from the environment, which can create misleading patterns on the screen that look like temperature variations but are actually reflections.
This means a thermal image of a pond or river looks like a fairly uniform thermal blob. You might see temperature gradients where warm water meets cold water, or where a spring feeds into a stream, but you won’t see individual objects beneath the surface. A large fish breaking the surface might briefly appear as a faint thermal trace, but only the exposed portion of its body would register, and only for the moment it’s actually out of the water.
The Exception: Mapping Where Fish Might Be
While thermal cameras can’t image fish directly, they can reveal water conditions that predict where fish congregate. The U.S. Fish and Wildlife Service uses airborne thermal cameras (known as FLIR, or Forward Looking Infrared) to study salmon habitat on Alaska’s Kenai Peninsula. These flights map surface water temperatures across rivers like the Funny River and Moose River, identifying cold-water refuges where spawning Chinook and Coho salmon tend to gather.
The logic is indirect but effective. Salmon are cold-water species that seek out specific temperature ranges during spawning. By flying a thermal camera over a river system, researchers can spot where groundwater springs or tributary inflows create pockets of cooler water. Those cool spots correlate strongly with fish presence, even though the camera never actually “sees” a single fish. Multiple flights throughout the open-water season help refine these maps and track how temperature patterns shift over time.
This technique works best in shallow, clear rivers where the surface temperature closely reflects conditions throughout the water column. In deeper or thermally stratified water, the surface reading may not represent what’s happening at depth where fish actually swim.
What Anglers Actually Use Thermal Cameras For
Despite the fish visibility limitation, thermal cameras have found a real niche in fishing, just not for spotting fish directly. Offshore anglers and commercial fishing operations use marine thermal cameras primarily for safety and navigation: seeing other boats, floating debris, channel markers, and shorelines in total darkness or fog. FLIR, the largest thermal camera manufacturer, markets its marine products almost entirely around nighttime visibility rather than fish finding.
Some experienced anglers use thermal imaging to locate bait balls near the surface, since a dense school of fish packed tightly at or just below the surface can create a faint thermal signature. Birds feeding on bait fish also light up clearly on thermal cameras, which helps locate offshore fishing spots at dawn or dusk. In freshwater, a thermal camera can help you find warmer inflows or spring-fed areas where fish tend to hold, especially in colder months.
For actually locating fish underwater, sonar remains the only practical technology. Sonar uses sound waves, which travel through water efficiently, rather than infrared radiation, which doesn’t. A basic fish finder bounces sound pulses off objects below and displays their depth and density. Modern side-scan and down-scan sonar can produce remarkably detailed images of fish, structure, and bottom contour. If your goal is to see what’s beneath the surface, sonar does what thermal physically cannot.
Thermal Sensitivity and Its Limits
Standard consumer thermal cameras can detect temperature differences of about 50 millikelvins (0.05°C). That’s sensitive enough to pick up subtle temperature variations on a water surface, like the warm wake left by a boat engine or temperature differences between a shaded bank and open water. But that sensitivity applies only to the surface film. No amount of thermal sensitivity helps you see through the water itself, because the infrared signal from below simply never reaches the camera.
Even in extremely shallow water (a few millimeters deep), like a fish splashing in a tidal flat, thermal imaging captures the water temperature rather than the fish’s body heat. The water layer, however thin, absorbs the infrared radiation from the fish and re-emits its own signature. You might detect a disturbance pattern as the fish moves warm or cold water around, but you’re seeing the water’s response, not the animal.