Lacus Aestatis (Latin aestātis, "Summer Lake") consists of two relatively small patches of smooth, interconnected lunar mare, located near the western limb of the Moon in the southwestern highlands.

[1] It was originally called Mare Aestatis but was renamed at the 1970 IAU convention.

[2] The selenographic coordinates of this feature are 15.0° S, 69.0° W, and it lies within a diameter of 90 km.

The other part lies to the southeast of the first, and forms an elongated, irregular patch that extends generally in a north-south direction.

Crater counts of this feature yield an age of 3.50 Gyr for the basalt, placing its formation in the Imbrian era.