Lake Tega, Reservoir in Chiba Prefecture, Japan.

Lake Tega is a shallow body of water in the northwest of Chiba Prefecture, stretching across two connected basins. The shoreline runs for 38 kilometers and hosts broad reed beds along with patches of lotus plants that float in the water throughout the year.

Lake Tega began as an inlet of the Katori Sea, called Tekanoura, until river sediment closed its mouth and formed a dammed lake. Under the Edo-period Tone River eastward diversion it became part of the Tone's lower course, and flooding led to reclamation: in 1727 the shogunate planned to drain the whole marsh, building the Senken dike and draining only the lower part. The dike collapsed in 1738. Postwar reclamation, completed in 1968, created about 500 hectares of rice fields and split the marsh into two basins.

The name Tega-numa appears in records from the Edo period, when the shogunate received two mallards and two swans from the lake as gifts in 1616. Today the great crested grebe is Abiko's city bird, and the Abiko City Museum of Birds and the Yamashina Institute for Ornithology stand near the shore. Local restaurants have served eel and carp dishes since the Edo period.

A 9.4 km greenway, the Kenritsu Teganuma Shizen Fureai Ryokudo, runs along the levee from Kitanakabashi in Kashiwa past the Michi-no-Eki Shonan roadside station to Tegaakebashi, with separate lanes for walkers, joggers and cyclists. Observation decks and rest stops along it look out over the water; 0.9 km from Tega Ohashi toward Akebashi the lotus colony can be seen. The Teganuma Koen park in Abiko marks the start of the lakeside walking route.

The lake has an average depth of just 86 centimeters, which encourages a dense network of submerged and floating plants. This shallow profile allows sunlight to reach the bottom, supporting a rich underwater flora.