Kami Izumi

Kami Izumi (神泉, God Spring) is a secluded spring near the outskirts of the Land of Water. Located underground, this legendary spring has remained undiscovered by the shinobi world, all except for one family, the Yaho of Kirigakure. The entryway is through an underwater cave-system just off of a small island and was discovered by mistake. Residing in the underground spring is Kami Izumi's Azure Water, along with a unique species of Crocodiles. How they ended up there is a complete mystery.

The Crocodiles are summonings capable of creating contracts and teaching their allies the art of Azure Water. What makes this water so special is not only because of it's bright blue hue; but because of the drastic burning sensation it can develop upon contact with the user's opponent, almost as if the water itself is on fire.

Overview
Only the Yaho Family know of Kami Izumi's existance. The easiest way to reach the spring is by having one of the crocodiles use the https://naruto.wikia.com/wiki/Reverse_Summoning_Technique. If that option is not available, the individual will simply have to make the journey themselves.