Lac à l'Eau Claire

Clearwater Lakes Lac à l'Eau Claire
Clearwater Lakes as seen from a Space Shuttle (North is top right)
Location	Baie-d'Hudson, Kativik, Quebec
Coordinates	56°08′N 74°18′W / 56.133°N 74.300°W / 56.133; -74.300Coordinates: 56°08′N 74°18′W / 56.133°N 74.300°W / 56.133; -74.300
Type	impact crater lake
Primary outflows	Clearwater River
Basin countries	Canada
Surface area	1,383 km2 (534 sq mi)
Max. depth	178 m (584 ft)
Surface elevation	241 m (791 ft)

The Lac à l'Eau Claire (the official name, in French), also called the Clearwater Lakes in English, is a calque of Wiyâšâkamî in Northern East Cree (changed form of wâšâkamî or wâšekamî in more southerly Cree dialects) and Allait Qasigialingat by the Inuit, are a pair of annular lakes on the Canadian Shield in Quebec, Canada, near Hudson Bay.

The lakes are actually a single body of water with a sprinkling of islands forming a "dotted line" between the eastern and western parts. The name is due to the clear water it holds. There are actually 25 lakes with that name in the province (26 if the Petit lac à l'Eau Claire — the Small Clearwater Lake — is included). These are the largest and northernmost, and the second largest natural lake in Quebec after Lake Mistassini.

In 1896, the explorer and geologist Albert Peter Low, a member of the Geological Survey of Canada, provided a probable explanation for the lakes' descriptive Cree name by highlighting the extraordinary clarity and depth of their icy waters.

The Clearwater Lakes occupy the near-circular depressions of two eroded impact craters (astroblemes). The eastern and western craters are 26 km (16 mi) and 36 km (22 mi) in diameter, respectively. Both craters were previously believed to have the same age, 290 ± 20 million years (Permian period), promoting the long held idea that they formed simultaneously. According to this doublet impact crater theory initially proposed by Michael R. Dence and colleagues in 1965, the impactors may have been gravitationally bound as a binary asteroid, a suggestion also made by Thomas Wm. Hamilton in a 1978 letter to Sky & Telescope magazine in support of the then-controversial theory that asteroids may possess moons (such as, for example, asteroid 243 Ida with its satellite Dactyl). However, repeated ⁴⁰Ar/³⁹Ar dating of impact melt rocks from both impact craters suggests that Clearwater East has an age of approximately 460–470 million years, corresponding to the Ordovician time period, whereas Clearwater West was formed 286.2 ± 2.6 million years ago, in the early Permian. Both Clearwater impact structures also carry different geophysical (natural remanent magnetization) signatures and different geochemical fingerprints of the impacting meteorite in the impact melt of each crater.