Nakaumi (中海) is a brackish lake located between Tottori and Shimane prefectures in Japan.

It is the fifth largest lake in surface area in Japan.

Nakaumi connects Lake Shinji (宍道湖 Shinji-ko) and the Sea of Japan, and is surrounded by the municipalities Matsue, Yasugi, Yonago and Sakaiminato.

Nakaumi is a brackish lake because it is connected to the Sea of Japan by a short channel, the Sakai Channel, and lies so low that the tides reverse the flow of the rivers all the way into Lake Shinji.

Nakaumi (中海) literally means "middle sea".