What is at the mouth of the Lena River, one of the great Siberian rivers which flows into the Arctic Ocean?

Question

The Lufra River and then the Lualaba River into which it flows are major headwaters (by volume) of the Congo River. Where do the rivers arise?

Answer 1

A delta (100 km (62 mi) by about 400 km (250 mi) wide)
The delta is frozen tundra for about seven months in each year, and a wetland when it melts. Part of it is protected as the Lena Delta Wildlife Reserve.