Lake Flagstaff, sometimes referred to as Flagstaff Lake is an ephemeral salt lake located in the Great Southern region of Western Australia, approximately 21 km (13 mi) north west of Woodanilling and 28 km (17 mi) south west of Wagin.

When they overflow waters discharge into the poorly described eastern branch of the Beaufort River.

[1] The northern shore of the lake is part of a crown reserve with an area of 1,047 acres (424 ha) designated for the protection of native fauna and flora.

[3] The traditional owners of the area are the Noongar peoples who have inhabited the region for tens of thousands of years.

Joe Douglas and his five sons all selected land there in the 1890s, building homesteads and farming.