Engineers in Jerusalem have discovered the largest underground water system ever found in Israel. The beneath the surface stream was unearthed near the Jerusalem convention center.

It was during excavation work by Israel Railways, that builders hit upon the opening of a cave that lead to the watercourse.

Researchers from the Cave Research Unit of the Hebrew University’s Department of Geography were called to the scene.

“It’s hard work, crawling through mud into a cave the end of which we haven’t reached yet,” Prof. Amos Frumkin, head of the unit, told Haaretz newspaper. Frumkin said the cave is between half a meter to a few meters wide, and is a few dozen meters high.

Researchers, who are still studying the cave, said it must be protected as a valuable natural phenomenon. They added that the preservation should not hamper or impede construction of the railway station.