Paul Robinson, age 10, of Peterborough, Ont., for his question:

How long is the Mackenzie river?

From its source in the Rocky Mountains to its mouth at the Arctic Ocean, the great Mackenzie travels a journey of 2,635 miles. It is Canada is greatest river. And in the whole of North America it is surpassed only by the Missouri‑Mississippi which, after all, is one of the three longest rivers in the world.

The great Mackenzie is fed by countless streams and by three huge lakes. In fact, on account of these lakes, it changes its name three times during its‑long journey to the cold Arctic Ocean. From its source to Lake Athabaska it is known as the Athabaska river. From Lake Athabaska to Great Slave Lake it is known as the Great Slave River. From Great Slave Lake, through Great Bear Lake and then to the Arctic it is known as the Mackenzie River ‑ named for Sir Alexander Mackenzie who explored this region at his own expense between 1889 and 1892.

During most of its journey, the great river is never narrower than half a mile and often several miles wide. It flows through countless miles of wild, unchartered forestland. Great Bear Lake, near the Arctic Circle is iced for nine months of the year and here the great river cuts through desolate tundra regions