[2][3][4][5] A monument at the east end of the lake is a key point in the demarcation of the northeast–southwest boundary between Ontario and Manitoba.

[6] Contrary to popular belief, this part of the inter-provincial border is not a mere straight line from the northeast corner of Manitoba's pre-1912 border to Hudson Bay.

Instead, the Manitoba Boundaries Extension Act, 1912 and the Ontario Boundaries Extension Act, 1912 define a corner at the east end of Island Lake (where the monument now sits) and from where the border continues to run in a slightly more north-south direction until it intersects with Hudson Bay at 89th meridian west.

Located on the lake are the First Nations communities of Wasagamack, St. Theresa Point and Garden Hill and the northern settlement of Island Lake which in 2011 had a combined population of 7,120.

About 18 km (11 miles) east across the bay are Garden Hill with a population of 2,776 and nearby Island Lake with 62 residents.