Is GPS tracking accurate for kayaking and rowing on open water?
Most of what makes a GPS track messy on land — a canopy of leaves, a street lined with tall buildings, a narrow canyon — simply is not there on a lake or a stretch of coastline. A phone on a kayak or a rowing boat usually has the cleanest view of the sky it will ever get. That does not mean the track comes out perfectly straight, and it does not mean every water activity behaves the same way once you are actually in the water rather than on top of it.
The short answer
For anything on the surface of the water — a kayak, a canoe, a rowing shell, a paddleboard — GPS accuracy is generally as good as it gets, often better than a typical hike, because there is nothing nearby to block or bounce the signal. For anything that puts the receiver underwater, even briefly and repeatedly, the story is completely different: GPS does not work underwater at all, for reasons that have nothing to do with weak signal or bad hardware.
Why open water is a good place for a receiver to be
GPS position is worked out by comparing signals from several satellites spread across the sky, and that calculation gets better the more of the sky a receiver can actually see. Tree cover scatters and blocks part of that view. Tall buildings block it on one or both sides and bounce signals off hard surfaces, arriving late and throwing the calculated position off. Open water has neither problem. A kayak in the middle of a lake or a rowing shell well off the coast gives a receiver close to the full dome of sky above it, uninterrupted, for as long as the activity lasts.
The one quirk that is specific to water
A flat, reflective surface can still bounce a satellite signal, the same underlying effect that causes trouble near glass and steel buildings, just far weaker. A signal arriving from a satellite low near the horizon can reflect off the surface of the water and reach the receiver a fraction of a second after the direct signal, and a receiver that cannot fully tell the two apart can be nudged slightly off its true position. This effect is small compared to the reflections a receiver deals with in a city, and satellites higher overhead are barely affected by it at all, but it is a real, water-specific source of noise rather than something borrowed from land-based GPS problems.
What often looks like an inaccurate track is really just drift
A kayak or a rowing shell does not sit still the way a hiker standing on solid ground does, and it does not always travel in the direction it is pointed. Wind pushes a light boat sideways. A current carries it downstream even during a pause to rest. None of that is a GPS error — the receiver is faithfully recording where the boat actually was, point by point, and a boat drifts in ways your feet on a trail simply cannot. A zigzag or a sideways bulge in a paddling track is very often the honest shape of being pushed around by water and wind, not a receiver getting confused.
Why swimming is a different problem entirely
GPS satellites broadcast on radio frequencies that water absorbs almost immediately — a receiver even a short distance below the surface has nothing to lock onto, no matter how clear the sky was a moment earlier. This is not a matter of degree the way tree cover or a nearby building is; underwater, there is no fix at all, full stop. A device carried by an open-water swimmer only gets a usable reading in the brief moments it clears the surface, such as during a breath or a stroke, and loses it again the instant it goes back under. A track recorded that way is built from a much sparser, more interrupted set of points than a walk, a ride, or a paddle ever produces, and gaps or straightened-out sections are the expected result of that interruption rather than a sign that anything is broken.
What this means in practice
- A phone kept dry on top of a kayak, canoe, or rowing shell — in a dry bag, a deck pocket, or mounted to the hull — tracks the whole outing with an unobstructed, water-level view of the sky.
- A boat drifting sideways in wind or current will show up as sideways movement on the recorded track, because that movement genuinely happened, not because the GPS was wrong.
- A device that spends the activity underwater, as it would while actually swimming, cannot maintain a GPS fix while submerged and will only pick up position at the surface.
- The occasional small nudge from a low-angle reflection off the water is a minor, water-specific effect, well short of the disruption caused by tree cover or a street lined with tall buildings.
Where TrailCam fits in
Rowing and swimming are two of the 11 activity types built into TrailCam, alongside hiking, cycling and the rest, each with its own colour on the map. Choosing one changes how the route is labelled and grouped afterwards; the GPS recording underneath runs the same way regardless of which activity is selected, which means the same open-water advantages and the same underwater limits apply no matter what the route is filed under. TrailCam is free to download.
Questions
- Does GPS work underwater at all?
- No. The radio signals GPS satellites broadcast are absorbed by water almost immediately, so a receiver below the surface cannot get a position fix regardless of how strong the signal was in the air a moment before.
- Is GPS more accurate on open water than on a hiking trail?
- Often, yes. Open water gives a receiver an unobstructed view of the sky, similar to a wide-open field, without the tree cover or building reflections that reduce accuracy on many land routes.
- Why does my kayaking or paddling track look zigzagged?
- Usually because the boat itself moved that way — pushed sideways by wind or current — rather than because the GPS made an error. A light, unpowered boat drifts in ways a walker on solid ground does not.
Recording your own routes
TrailCam is an iPhone app that records your route with GPS, keeps video clips, photos and voice notes pinned to the spot where you took them, and exports the result as GPX 1.1 or CSV. It is free to download.