Flathead Lake is about 1.2 times smaller than Saint Lucia.

Saint Lucia is approximately 616 sq km, while Flathead Lake is approximately 510 km² (197 sq mi), making Flathead Lake 82.79% the size of Saint Lucia.
Tip: This to-scale comparison of Saint Lucia vs. Flathead Lake uses the Mercator projection, which distorts the size of regions near the poles.
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