Pozo Azul

El Pozo Azul de Covanera - El Pozo Azul

Useful Information

Location: Covanera, Burgos.
90 km south of Santander. Follow N-623 along Rio Rudrón, in Covanera take single lane bridge across the river, then left 300 m to small parking lot. Walk 300 m (5 minutes) up the side valley.
(42.735772, -3.795994)
Open: no restrictions.
Fee: free.
Classification: KarstVauclusian Spring SpeleologyKarst cave
Dimension: L=13,755 m, T=11 °C (water).
Spring: D=9 m.
1st siphon S1: L=700 m, D=-21 m.
Aerial gallery G1: L=300 m (The bubble).
2nd siphon S2: L=5,160 m, D=-71 m.
Aerial gallery G2: L=90 m (Tipperary) + 1,700 m Dry gallery ( G. Covanera) + 300m + 300m.
3rd siphon S3: L=3,725 m, D=-40 m (3,275m of siphon gallery + a lateral siphon of 450 m).
Aerial gallery G3: L=180 m (Razor Passage).
4th siphon S4: L=140 m, D=? m.
G4 aerial gallery : L=300 m (Razor II Passage).
5th siphon S5: L≈100m, D=?m.
Aerial gallery G5: L=300m, VR=300m.
6th siphon S6 : L=160m, D=-40m.
Guided tours: self guided
Photography: allowed
Accessibility: no
Bibliography: E. Sanz Pérez, J. Medina Ferrer (1986): The underground karst morphology of the Pozo Azul (Burgos) Conference on karst in the Basque Country. pp. 307-322.
Martyn Farr (2011): Its a Long Way from Tipperary, Descent 217, Dec/Jan 2011.
Scoff (2016): Pozo Azul, Bradford Pothole Club (BPC) : BulletinVol 7 No 6 (Jun 2016).
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.


NOV-1964 exploration of the first 100 m by Joaquín Plana and Pedro Plana from G.E. Edelweiss.
1966 Joaquín Plana reaches 200 m and breaks the world record for underwater caving.
1979 first sump crossed the first time by Carmen Portilla and Fernando Fuentes from the G.E. Standard (STD) from Madrid.
1981 second sump reached after the exploration of the subaerial section and explored for 70 m/-27 m.
1983 383 m of sump 2 reached by G.E. Standard.
1989 G.E.Gaia advances to 650 m.
SEP-2002 sump 2 extended to 1,950 m and a depth of -60 m by Jason Mallinson.
MAY-2004 sump 2 extended to 2,220 m and a depth of -70 m by Jason Mallinson.
SEP-2010 British-led expedition with Martyn Farr reaches 8.8 km of underwater travel, the world's longest cave diving penetration.
2011 sump 3 passed after 3,275 m to find an active streamway and a fourth sump.
2013 sump 4 only 140 m long, fast flowing river canyon explored for 300 m.
2014 sump 5 discovered, dive distance 9,375 m and the total cave passage 12,000 m.
2015 sump 6 discovered and dived.


Pozo Azul (Blue Pot) is a deep blue karst spring, as the name suggests. The blue colour is a result of sunlight which is filtered by the limestone rich water. So it is best visited on a sunny day around midday or during afternoon. The colour is typical for karst springs, if they are deep enough. The spring is much visited by tourists, although it is actually not signposted. If it is crowded and the small parking lot at the spring full, there are two large parking lots at Covanera on the other side of the river. Its just 400 m additional walk.

The cave behind the spring is filled with water and only accessible to cave divers. The small brook it creates is a tributary to Río Rudrón and only 300 m long. But this side valley is quite impressive, limestone cliffs and rocks created by the river erosion and karren. There is little vegetation due to the semi-arid climate to obfuscate the geology. It seems the 300 m long side valley is actually a former cave, which collapsed and was eroded. The retrograde valley incision follows the cave by continually weathering the rocks arounf the spring and transporting them away with the river.

The water of the spring emerges from a huge cave, starting with a 700 m/-21 m sump. Since the first exploration by Joaquín Plana from G.E. Edelweiss in 1964 this cave is a cave diving mekka of Spain. But diving is difficult, the first attempt made only the first 100 m. Around 1980, with better diving technology they crossed the first 700 m sump and discovered a 300 m long air filled river passage with a cascade, and after that a second sump is reached. This second sump is 5,160 m long at a depth of -71 m and was the longest sump in Spain after its discovery. After another air filled passage of 90 m the third sump is reached which was dived by Martyn Farr in 2012 for 2,965m. He is one of the most famous cave divers of the world, not only because of his dives, but also because he published several books about cave diving.

In the next years the known cave grew constantly, while the difficulties grew exponentially. But the difficulties were at least partly compensated by advancements in diving technology. Nevertheless, the cave is today the "Mount Everest" of European cave diving. And most tourists visiting the small pond have no idea.