In 1783 the North West Fur Company was formally established, and after a severe struggle obtained, owing mainly to the efforts of Alexander Mackenzie, a fair share of the trade in the west of the region controlled by the Hudson's Bay people. Mackenzie was at Fort Chippewyan, on Lake Athabasca, and thence he was sent in 1789 on an exploring voyage to the north. In four birch-bark canoes, one of his party being an Indian known as English Chief, who had been with Hearne on his journey to the Coppermine, he started down the Great Slave River into the Great Slave Lake. After spending twenty days in crossing and exploring this vast sheet of water, he entered the large river now bearing his name, and down it amid many dangers and difficulties, overcome by skill, persuasion, force, good humour or good fortune, he reached the sea on the 14th of July. He camped on Whale Island, the name being given owing to one of the men sighting a great many animals in the water, which he at first supposed to be pieces of ice. "However," says Mackenzie, "I was awakened to resolve the doubts which had taken place respecting this extraordinary appearance. I immediately perceived that they were whales; and having ordered the canoe to be prepared, we embarked in pursuit of them. It was indeed a very wild and unreflecting enterprise, and it was a very fortunate circumstance that we failed in our attempt to overtake them, as a stroke from the tail of one of these enormous fish would have dashed the canoe to pieces. We may, perhaps, have been indebted to the foggy weather for our safety, as it prevented us from continuing our pursuit. Our guide informed us that they are the same kind of fish which are the principal food of the Eskimos, and they were frequently seen as large as our canoe. The part of them which appeared above the water was altogether white, and they were much larger than the largest porpoise"—being evidently belugas (_Delphinapterus leucas_). Satisfied with a short canoe voyage on the sea, he returned to the river and made his way back to the fort, arriving there in the middle of September. He had thus proved the existence of the sea twenty degrees further west than Hearne had done. Three years afterwards he started on his notable journey to the Pacific at Cape Menzies, facing Princess Royal Island, being the first white man to cross the Rocky Mountains, and, as he had reached Fort Chippewyan by way of Montreal, the first to cross North America above the Gulf of Mexico.