Sisovatnet

or is a lake that lies in the municipality of Sørfold in Nordland county, Norway. It is located in the southeastern part of the municipality of Sørfold, about 10 km east of the village of Straumen. The lake Rundvatnet lies immediately east of Sisovatnet.

The lake is fed by the melting snow from the large Blåmannsisen glacier to the southeast. Water naturally flows out of Sisovatnet to the lake Andkjelvatnet, although much of the water is diverted to the lake Straumvatnet to be used for hydroelectric power.