Hinuma is a lake about 10 kilometers (6 miles) southeast of Mito. It has a circumference of 22 kilometers (14 miles) and an area of 10 square kilometers (4 square miles). Sea water flows into the lake through the river Nakagawa. Therefore, it's home to around 60 species of both freshwater and saltwater fish.

The lake is part of the Oarai Prefectural Natural Park, which stretches from the lake to Oarai Beach on the Pacific.