The encierro does not wait for weather. On mornings when rain falls on the medieval streets of Pamplona, or when dew clings to the adoquines, or when the city has just finished spraying down the stones to clean them, the encierro runs exactly as scheduled. What changes is not whether the run happens, but how it unfolds. Rain fundamentally alters traction, bull behavior, and the way an experienced runner must position themselves to survive it. This is where the difference between running in dry conditions and wet conditions becomes a matter of survival. For the full breakdown of the 875-meter course, see our guide to the complete encierro route.
The first misconception many first-time runners hold is that the encierro will be cancelled or delayed because of rain or storms. Dennis notes that the run has never been postponed for weather in living memory. “They don’t delay it due to weather or to storm. Never had that.” The encierro runs in rain, snow (rare in July), or sunshine. This is a fundamental fact of San Fermin preparation that separates someone who has researched the event from someone who showed up hoping for fair weather.
Why Rain Makes the Route Dangerous
The adoquines (cobblestones) that make up the majority of the encierro route transform when wet. Centuries-old stone becomes slick. The groove patterns that collect water in dry conditions now funnel standing water across the route. Modern paved sections that were resurfaced in the 1990s become treacherous. The surface that provides adequate traction on a dry morning becomes a liability when rain or dew reduces friction. Okdiario’s encierro photography has captured moments where wet cobblestones contributed to runner falls at critical choke points.
For the bulls, rain is even more problematic than it is for runners. Steers use their hooves to gauge the route and adjust their footing, just as runners do. When the ground beneath them is slick, they lose confidence in their own movement. Their stride becomes choppy. They slip. And unlike humans, a 500-plus-kilogram animal cannot recover its balance as easily when its feet lose contact with the ground.
The danger is not purely mechanical. Rain also means reduced visibility for both runners and the herd. Water on stone creates reflections that distort depth perception. The narrow canyon-like streets of the casco viejo become darker when clouds hang low. Runners who position themselves based on visual markers—where they can see the turn coming, where they can gauge distance to the wall—lose those reference points.
The Contradiction of Wet Conditions
There is a paradox at the heart of rainy encierros: the route is often wet even on mornings when no rain has fallen. Dennis explains this contradiction: “The route will still be a little wet just because they’ve had to spray down the streets. And because it’s early morning and the sun isn’t shining through most of the cavernous streets of the route. There’s no opportunity for that water to evaporate.”
The city of Pamplona sprays the encierro route in the early morning hours before the run begins. This is done for cleanliness and to prepare the surface, but it has a side effect. In the narrow, shadowed streets of the medieval quarter, sunlight does not penetrate. Water applied at 5:00 AM is still there at 8:00 AM when the run begins. It may not rain, but the route is wet. As sanfermines.net details, these preparations are part of a broader protocol to manage conditions on the route each morning.
Additionally, the previous evening’s festivities leave residual moisture. Restaurants and bars along the route empty their water buckets onto the streets. Revelers urinate in corners. Cleaning crews hose down balconies and storefronts. By early morning, before the spray trucks arrive, sections of the route already have a film of moisture.
Bull Behavior Changes When Traction Fails
A wet encierro is not simply a faster or slower version of a dry one. The herd’s behavior changes. In Ray Mouton’s historical account Pamplona (2002), the consequence of the 1990s resurfacing is documented: the steers “who know the route well and normally navigate the course without incident have been slipping, sliding, and falling down” on wet mornings. Since the paving, the issue has only been addressed by applying anti-slip treatment to certain sections.
When bulls lose their footing, they become unpredictable. A steer that would normally run straight ahead may veer left or right searching for better traction. A herd that would normally stay grouped may split. Individual animals may panic. And a panicked bull on slick stones is less predictable than one running confidently down a dry street. Diario AS has reported on multiple encierros where wet conditions led to separated bulls and extended run times.
Dennis notes that the city applies anti-slip solution at La Curva de Estafeta specifically to address this: “To help with the slipperiness, they put the anti-slip solution down again at La Curva de Estafeta. To try to help with traction for the bulls themselves.” This treatment is not for the comfort of runners. It is for the bulls’ safety and the route’s function. The treatment cleans the pores of the stone and restores grip, but it is localized. The rest of the route remains subject to whatever moisture is present. Read more about why this stretch matters in our guide to Calle Estafeta.
Specific Sections That Become Hazardous
Not every section of the encierro is equally dangerous when wet. Some stretches are wide and relatively flat. Others are narrow, angled, or have physical features that create hazard zones.
Santo Domingo is always hazardous in wet conditions. The steep slope becomes a slide. The curbs that remain on this section catch runners’ feet. The band of white limestone on the left side of the slope, already noted for being slippery in dry conditions, becomes a skating rink. A runner who falls on Santo Domingo is falling uphill or downhill with momentum. Recovery is difficult.
La Curva de Mercaderes, the sharp right turn where the route transitions from Mercaderes to Estafeta, is another critical hazard zone. The turn itself demands traction and body control. In wet conditions, runners pile up here. Momentum that would be manageable on dry stone carries runners into the corner with reduced braking power. The anti-slip treatment helps, but the curve is still a point of compression and risk.
The callejon, the narrow funnel leading into the tunnel at the end of the route, becomes more dangerous when wet not because of the surface itself but because of congestion. Runners crowd this section desperately trying to stay in front of the bulls. When stone is slick, crowding becomes a collision hazard. Runners trip over each other rather than over the ground.
Why Some Runners Actually Prefer Rain
This seems counterintuitive, but Dennis points out that rain has a hidden advantage for experienced runners: “Often, some runners will stay away from the route on a rainy day, thinking that it might be more dangerous. Luckily, I think that allows the route to be a bit more open and give runners a bit more space.”
When the forecast calls for rain, many first-time runners and casual participants opt out. They believe the risk is too high. They believe the run is more dangerous. This belief, correct in a technical sense, creates an unexpected tactical advantage. The route becomes less crowded. There is more space to run. More space means fewer collisions, fewer pile-ups, and more room to position yourself strategically.
Dennis adds: “For an experienced runner that can be a benefit. That can be seen as a benefit.” An experienced runner who understands wet traction, who knows how to adjust footwork, and who is comfortable running in rain might choose the rainy morning precisely because fewer runners have shown up. This is not the choice for first-timers or those unprepared for slippery conditions, but for someone who has run the route multiple times, rain can mean less human congestion and more control.
Expert Insight: Dennis Clancey on Wet Encierros
“The encierro is never cancelled or delayed for rain or storms. Often, some runners will stay away on rainy days, which means the route is more open and gives runners more space. For an experienced runner, that can be a benefit. But you need to understand that the route will still be wet regardless of whether it rains, because the city sprays the streets in the early morning and the sun can’t evaporate that water in the narrow medieval streets. The anti-slip solution is applied at La Curva de Estafeta specifically to help the bulls with traction.”
— Dennis Clancey, founder of Encierro and member of La Unica Pena
For a comprehensive visual guide to running the route in any conditions, watch Dennis Clancey’s Definitive Guide to Running with Bulls, available in 16 languages:
Dennis has run the encierro since 2007 and has experienced every weather condition the event throws at runners. His experience shows that preparation for wet conditions is not a luxury; it is a necessity. Rain happens. Dew happens. The route is always somewhat wet. Runners who show up unprepared for slippery cobblestones are unprepared for the encierro as it actually exists, not as they imagine it.
Spanish Vocabulary
Adoquin (ah-doh-KEEN): A cobblestone or paving stone. The plural, adoquines, refers to the cobblestone surface that becomes slippery when wet.
Callejon (kah-yeh-HONE): A narrow alley or passageway. The callejon at the end of the encierro route becomes crowded and dangerous in wet conditions because runners lose traction while trying to stay ahead of the bulls.
Desliz (des-LEEZ): A slip or slipping. The word captures the loss of traction that wet adoquines create.
Curva (KUR-vah): A curve or turn. La Curva de Mercaderes and La Curva de Estafeta are the two major turns on the route, both particularly hazardous in wet conditions.
Frequently Asked Questions
Does the encierro run if it rains?
Yes, always. The encierro has never been cancelled or delayed for rain, snow, or any other weather. If you are running the encierro, you must be prepared for any weather condition that might occur on race morning.
Why is the route wet even when it hasn’t rained?
The city sprays the route in the early morning before the encierro begins. Additionally, the medieval streets of Pamplona are narrow and shaded, so water applied in the early morning cannot evaporate before the run starts at 8:00 AM. Residual moisture from the previous night’s festivities also contributes.
What sections are most dangerous in wet conditions?
Santo Domingo, the steep slope at the beginning, is particularly hazardous because of its grade and the limestone band that becomes slippery. La Curva de Mercaderes is dangerous because the turn demands traction that is difficult to maintain on wet stone. The callejon becomes hazardous because of runner congestion combined with reduced traction.
Is the encierro more dangerous when it rains?
Yes, reduced traction makes the route more dangerous for both runners and bulls. However, some experienced runners prefer rainy mornings because fewer casual runners participate, leaving the route less crowded.
How does rain affect the bulls?
Bulls rely on hooves for traction and balance. On wet stone, steers lose confidence and may slip or fall. They become less predictable. This is why the city applies anti-slip treatment at critical turns.
What shoes should I wear for a wet encierro?
Traction on wet stone is even more critical than on dry stone. Trail shoes with aggressive lugs, or minimalist shoes with vibram soles specifically designed for stone, are both better choices than smooth-soled shoes. Lace them very tightly.
The encierro in rain is a real risk that requires real preparation. Do not assume you can run a wet encierro the same way you would run it dry. To understand every section of the route and how conditions affect each one, read our complete guide to the encierro route. For specific guidance on running Calle Estafeta, the longest straight on the course, visit our guide.