|Location:||Covanera, Burgos. 90 km south of Santander.|
|Dimension:||T=11 °C (water)|
|As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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|NOV-1964||exploration of the first 100 m by Joaquín Plana from G.E.Edelweiss.|
|1979||first sump crossed the first time by two divers from the G.E. Standard (STD) from Madrid.|
|1981||second sump reached after the exploration of the subaerial section.|
|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.|
Pozo Azul (Blue Pot) is a deep blue karst spring, as the name suggests. It is much visited by tourists. The cave behind the spring is filled with water and only accessible to cave divers.
The water of the spring emerges from a huge cave, starting with a 700 m sump. After a 300 m swim, a cascade, and a short stream passage a second sump is reached. This second sump is known for 2,220 m and a depth of -70 m and is the longest sump in Spain.