The Zarqa River (Arabic: نهر الزرقاء, Nahr az-Zarqāʾ, lit. "the River of the Blue [City]") is the second largest tributary of the lower Jordan River, after the Yarmouk River. It is the third largest river in the region by annual discharge and its watershed encompasses the most densely populated areas east of the Jordan River. The Zarqa rises in springs near Amman, and flows through a deep and broad valley into the Jordan, at an elevation 1,090 metres (3,580 ft) lower. At its spring lays 'Ain Ghazal (Arabic: عين غزال), a major archaeological site that dates back to the Neolithic. Archaeological finds along the course of the river indicate the area was rich in flora and fauna in the past. The river is heavily polluted and its restoration is one of the top priorities for the Jordanian Ministry of the Environment. Geologically, the Zarqa River is about 30 million years old. It is well known for its amber deposits that date back to the Hauterivian era of the Early Cretaceous, 135 million years ago. A remarkable flora and fauna was reported from this amber reflecting tropical paleoenvironmental conditions prevailing during the time of resin deposition. The Zarqa River is identified with the biblical river Jabbok.[4] Biblical Jacob crossed the Jabbok on his way to Canaan, after leaving Harran. It leads west into the Sukkot Valley, from where one crosses over the Jordan and can easily reach Shechem, as Jacob eventually did. The biblical cities of Zaretan and Adam are also at the mouth of the valley. The river is first mentioned in the Book of Genesis in connection with the meeting of Jacob and Esau, and with the struggle of Jacob with the angel.[5] It was the boundary separating the territory of Reuben and Gad from that of Ammon,[6] the latter being described as lying along the Jabbok.[7][8][9] The territory of Sihon is described as extending "from Arnon unto Jabbok" (Numbers 21:24), and it was reclaimed later by the King of Ammon.Eusebius places the river between Gerasa and Philadelphia.