The Gulf of Ob (also known as Ob Bay) is a bay of the Arctic Ocean, located in Northern Russia at the mouth of the Ob River. It is the world's longest estuary. The mouth of the Gulf of Ob is in the Kara Sea between the Gyda and Yamal peninsulas. It is about 1,000 km (620 mi) long and varies in width from about 50 to 80 km (31 to 50 mi).

It generally runs north and south. The gulf is relatively shallow, with an average depth from 10 to 12 metres (33 to 39 ft), 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, such as Khaley Island. 

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, such as Khalevigo and Nyavigo, the Gulf of Ob is free of islands until it meets the Kara Sea.

According to en.wikipedia