Your feet would need to strike the water surface at more than 30 meters per second, which works out to roughly 67 mph. That figure comes from hydrodynamic modeling of what it takes for a human-sized body to generate enough upward force with each foot slap to avoid sinking, and it would demand about 15 times the muscle power a person actually has available. The number sounds absurd because it is: water running is one of those feats where biology and physics conspire to make the answer “not possible for humans on Earth,” though the reasons are more interesting than the headline.
What the 67 MPH Figure Actually Means
The speed that matters for water running is not how fast you move forward across the surface. It is how fast each foot impacts the water on the way down. When researchers modeled a human trying to replicate the water-running behavior of basilisk lizards, they calculated that each foot would need to slap the surface at speeds exceeding 30 m/s to generate enough upward impulse to support an average person’s body weight. That slap speed, converted for anyone thinking in miles per hour, lands around 67 mph.1PubMed Central. Running in Place on Water at Simulated Reduced Gravity
To put that in perspective, 67 mph is faster than the terminal velocity of a falling baseball and well beyond any speed a human leg can produce voluntarily. The estimate also assumed that a person would need roughly 15 times the muscular power output available to the human body. So the barrier is not just foot speed but raw power: even if you could somehow swing your legs that fast, your muscles could not sustain the force needed to keep doing it step after step.1PubMed Central. Running in Place on Water at Simulated Reduced Gravity
Why Water Running Is So Physically Demanding
Running on solid ground works because the ground pushes back with an equal and opposite force every time your foot lands. Water does not do that. It yields. The only way to stay above the surface is to push water downward fast enough and frequently enough that the reaction forces keep your body aloft before you sink. You are essentially creating your own “ground” with each step, and that ground disappears the instant you stop pushing.
Studies of basilisk lizards, the most famous water runners in nature, show that the process involves two phases per step. The first is the slap: the foot hits the surface hard, driving water downward and creating a pocket of air beneath the foot. The second is the stroke: the foot pushes further down through the water while that air cavity is still open, generating additional upward force. The lizard then yanks its foot back out before the cavity collapses around it, which would create downward suction.2Nature. A hydrodynamic model of locomotion in the Basilisk Lizard For intermediate-sized basilisks weighing about 90 grams, most of the weight support comes from that stroking phase rather than the initial slap. The slap alone is not enough to hold up even a small lizard.
For a human, the problem is scale. The force generated by slapping water depends on the area of whatever is doing the slapping and the speed of impact. A basilisk lizard weighs a fraction of a kilogram and has proportionally large, fringed feet relative to its body weight. A human weighing 60 to 80 kilograms has comparatively tiny feet for the mass they would need to support. You would need either absurdly large feet or absurdly fast leg movements to compensate, and the math says the speed required is beyond human physiology.
How Basilisk Lizards Manage It
Basilisk lizards run across water at forward speeds of roughly 1.3 meters per second, just under 3 mph. That leisurely-sounding pace is misleading. What matters is how fast their feet move vertically, and juvenile lizards in particular produce their greatest support and propulsive forces during the first half of each step, when the foot is driving straight down into the water.3PubMed Central. Running on water: Three-dimensional force generation by basilisk lizards They also generate large sideways forces that shift from inward to outward throughout the step, acting as a kind of dynamic stabilizer that keeps them from tipping.3PubMed Central. Running on water: Three-dimensional force generation by basilisk lizards
There is a catch even for basilisks: body size matters enormously. Small juveniles can sprint across ponds with relative ease. Larger adults, which can exceed 200 grams, struggle more and tend to sink sooner. The physics scales unfavorably because mass increases with the cube of body length while foot surface area only increases with the square. Every time a basilisk doubles in size, the challenge of staying on top of the water gets disproportionately harder. This is the same scaling problem that makes the feat flatly impossible for a creature as large as a human.
Grebes Use a Completely Different Strategy
Basilisk lizards are the textbook example of water running, but they are not the only animals that do it. Western and Clark’s grebes, which are sizeable waterbirds weighing over a kilogram, run across the surface during elaborate mating displays. At first glance this seems like it should be even harder than what basilisks do, since the birds are much heavier. But grebes have evolved a qualitatively different approach.4PubMed. Western and Clark’s grebes use novel strategies for running on water
Grebes reach stride rates of up to 10 steps per second, which is exceptionally fast. Their feet are large and lobed, and the high speed at which those feet hit the water allows them to generate 30 to 55 percent of the weight support they need from the slap phase alone. That is a much higher proportion than basilisk lizards achieve with slapping. Their foot bones are also flattened in a way that reduces drag on the upstroke, letting them pull each foot out of the water sideways rather than straight up. This avoids the suction problem that basilisks deal with by retracting the foot before the air cavity collapses.4PubMed. Western and Clark’s grebes use novel strategies for running on water
Grebes also get an assist from their wings, which provide some lift during the rushing display. A human has no such option. The grebe strategy is a reminder that water running, even in nature, requires a whole suite of anatomical and behavioral adaptations tuned to the animal’s specific body plan. No single trick makes it possible.
What If Gravity Were Lower?
Since the fundamental barrier for humans is the ratio of body weight to available muscle power, one obvious question is whether reducing that weight changes the picture. It does. Researchers tested this by having people run in place on a wading pool while suspended in a harness that progressively unloaded their body weight. The results confirmed what the theoretical models predicted: at gravity levels equivalent to about 22 percent of Earth’s pull or less, a human wearing small rigid fins can run on water without sinking.1PubMed Central. Running in Place on Water at Simulated Reduced Gravity
Twenty-two percent of Earth’s gravity is slightly higher than lunar gravity, which sits at about 16.5 percent. So on the Moon, if there were an open body of liquid water, a person with foot fins could plausibly run across it. The fins increase the effective surface area of the foot, doing artificially what the basilisk lizard’s fringed toes do naturally. Without the fins, even lunar gravity is not quite enough for human-sized feet to generate sufficient force.
This experiment is interesting not because anyone is planning to run across lunar lakes, but because it pins down exactly where the physical threshold sits. Earth gravity is about 4.5 times too strong for human water running. That gap is too large for any realistic enhancement of foot size or leg strength to close on its own.
The Cornstarch Loophole
Videos of people running across pools filled with a cornstarch-and-water mixture pop up regularly online, usually with the implication that a non-Newtonian fluid “lets you walk on water.” The reality is more nuanced. A dense cornstarch suspension is a shear-thickening fluid: it flows like a liquid under gentle handling but stiffens dramatically under sudden impact. When you stomp on the surface, the suspension temporarily jams into a solid-like state beneath your foot, and that jammed region can support significant weight.
Lab measurements of these suspensions show that they can support normal stresses on the order of megapascals under impact, which is substantial. The key finding is that the stress increase happens when a dynamically jammed region propagates all the way from the impact point to the bottom of the container. In other words, the pool needs a solid floor for the jammed column of cornstarch to push against. Without that rigid boundary, the trick does not work nearly as well.5PubMed Central. Constitutive relation for the system-spanning dynamically jammed region in response to impact of cornstarch and water suspensions
So while the cornstarch pool looks like water running, it is really a different phenomenon. You are not generating hydrodynamic lift the way a basilisk lizard does. You are jamming a suspension against a solid surface. The pool depth, the cornstarch concentration, and the presence of a hard bottom all matter. Try the same thing in a deep lake filled with slightly diluted cornstarch water and you would sink. The stunt is real physics, but it does not answer the water-running question in any meaningful way.
Robots That Run on Water
Engineers have taken the basilisk lizard’s trick and tried to replicate it mechanically. Multiple research groups have built small bipedal robots that use linkage mechanisms to reproduce the lizard’s foot trajectory: a fast downward slap, a stroke through the air cavity, and a quick retraction. One such robot, weighing 160 grams, generated a maximum lift of 2.4 times its own weight and achieved forward speeds of 0.3 to 0.8 meters per second on the water surface.6PubMed. Design of a bipedal robot for water running based on a six-linkage mechanism inspired by basilisk lizards A separate robot design using a different linkage mechanism, weighing 320 grams, produced an average propulsion force of about 1.3 newtons and maintained its balance at a body tilt angle of only 5 degrees.7Journal of Bionic Engineering. A Bio-Inspired Biped Water Running Robot Incorporating the Watt-I Planar Linkage Mechanism
These robots succeed because they are small and light, just like the basilisk lizards they mimic. No one has built a human-scale water-running robot. The scaling problem that defeats biological water runners defeats mechanical ones too: making the robot bigger requires disproportionately more power, larger feet, and faster leg cycles. At human scale, the engineering challenge converges on the same physical constraints that make biological water running impossible for us. The robots are useful as proof that the underlying biomechanics can be replicated artificially, but they do not point toward a wearable device that would let a person sprint across a lake.
How Fast Other Animals Move on or Near the Surface
Water running sits on a spectrum of surface-related locomotion strategies in nature. Basilisk lizards and grebes are the clearest examples of animals that actually run on the water surface using hydrodynamic forces. But other animals interact with the air-water boundary in ways that involve impressive speed and power output.
Dolphins, for instance, can lift most of their body above the surface using tail beats alone. When two-thirds of a dolphin’s body is out of the water, the tail beats at about 2.57 beats per second, equivalent to the rate used when swimming at roughly 20 km/h (about 12 mph). The thrust generated ranges from about 289 to over 1,260 newtons, enough to support nearly 130 kilograms of body weight above the waterline.8Journal of Experimental Biology. Dolphins beat tails faster to stand up in water Dolphins are not running on the surface, but the power required to hold that much mass above water illustrates just how demanding it is to fight gravity at the boundary between air and liquid. A human trying to stand on water would need comparable or greater force production from legs alone, without the benefit of a hydrodynamically optimized tail working in the most efficient medium available.
At much higher speeds, the physics of water impact changes character entirely. When an object hits water at about 14.1 meters per second (roughly 32 mph), the local pressure can drop below water’s vapor pressure, causing cavitation: the formation of tiny vapor bubbles that collapse violently. This threshold is relevant to torpedo and propeller design but has never been clearly observed in animal dives, even among seabirds that plunge from great heights.9PubMed Central. Water entry and exit in nature: review The 67 mph foot-slap speed required for human water running would blast past the cavitation threshold, meaning each step would produce violent bubble collapse around the foot. Even in a hypothetical scenario where a person could move their legs that fast, cavitation damage to the foot would be a serious problem nobody talks about.
Why the Question Keeps Coming Up
The fascination with running on water has deep cultural roots, but the persistence of the question in a scientific context comes from something more specific: the answer is almost reachable. The gap between human capability and the physical requirement is large (a factor of 15 in power), but not so large that it feels like asking whether a person could fly by flapping their arms. Basilisk lizards prove the physics works at small scales. Grebes prove it works at larger scales than you might expect. Reduced-gravity experiments prove humans can actually do it when the weight problem is reduced. And cornstarch pools prove that changing the fluid’s properties can make it trivially easy.
Each of these partial successes makes the full feat feel tantalizingly close, when in reality the scaling laws of hydrodynamics push it firmly out of reach. A person would need feet roughly the size of trash can lids, legs that cycle at several times their actual speed, and muscles that produce an order of magnitude more power than they can. No plausible combination of training, footwear, or technique bridges that gap on Earth. The 67 mph answer is the physics shorthand for a set of constraints that all point in the same direction: humans are too heavy, too slow, and too weak to run on water, and each of those deficits alone would be disqualifying.