The Gulf of Ob is a gigantic bay of the Arctic Ocean, located in Northern Russia at the head the mouth of the Ob River. This Gulf flows into the Kara Sea between the Gydan and Yamal peninsulas. It is about 1,000 km (600 mi) long and varies in width from about 50 km (30 mi) to 80 km (50 mi), and generally runs north and south. It is relatively shallow, with an average depth from ten to twelve metres which restricts heavy sea transport. The Taz Estuary is an eastern side-branch formed by the Taz River. There are several islands near the mouth of the Ob, at the beginning of the estuary, like Khaley. All these islands are close to the shore and they are generally flat and low-lying. They are protected wetlands under Ramsar. Further north, except for a few islands located close to the shore, like Khalevigo and Nyavigo, the Gulf of Ob is free of islands until it meets the Kara Sea.