A week of travel brought them on June 9 to the Great Slave Lake. It was still early in the season. The rigour of winter was not yet relaxed. As far as the eye could see the surface of the lake presented an unbroken sheet of ice. Only along the shore had narrow lanes of open water appeared. The weather was bitterly cold, and there was no immediate prospect of the break-up of the ice. For a fortnight Mackenzie and his party remained at the lake, skirting its shores as best they could, and searching among the bays and islands of its western end for the outlet towards the north which they knew must exist. Heavy rain, alternating with bitter cold, caused them much hardship. At times it froze so {78} hard that a thin sheet of new ice covered even the open water of the lake. But as the month advanced the mass of old ice began slowly to break; strong winds drove it towards the north, and the canoes were presently able to pass, with great danger and difficulty, among the broken floes. Mackenzie met a band of Yellow Knife Indians, who assured him that a great river ran out of the west end of the lake, and offered a guide to aid him in finding the channel among the islands and sandbars of the lake. Convinced that his search would be successful, Mackenzie took all the remaining supplies into his canoes and sent back Leroux to Chipewyan with the news that he had gone north down the great river. But even after obtaining his guide Mackenzie spent four days searching for the outlet It was not till the end of the month of June that his search was rewarded, and, at the extreme south-west, the lake, after stretching out among islands and shallows, was found to contract into the channel of a river.