The Kaunissaare Reservoir () is a lake in Estonia. It is located on the Jägala River in the village of Kaunissaare in Anija Parish, Harju County, near Kehra.
The reservoir is part of the Tallinn water supply system and is connected to the Pirita, Soodla, and Aavoja rivers via canals.
The lake has an area of , and it has three islands with a combined area of . The lake has an average depth of and a maximum depth of . It is long, and its shoreline measures . It has a volume of .
The construction of the reservoir took place between 1980 and 1984. A fish passage was built between the reservoir and downstream Jägala River in 2015.