| Unterwarnow | |
|---|---|
View to the City of Rostock | |
| Location | Baltic Sea |
| Coordinates | 54°06′14.7″N 12°06′14.9″E / 54.104083°N 12.104139°E |
River sources | Warnow |
Ocean/sea sources | Atlantic Ocean |
| Basin countries | Germany |
| Max. depth | 13 m (43 ft) |
| Salinity | ~10‰ |
| Settlements | Rostock |

Unterwarnow is the estuary of the Warnow River in Mecklenburg-Vorpommern, northern Germany. It connects with the Baltic Sea in Warnemünde. The city of Rostock is located on its banks.
The part of the riverbed near the river mouth is deepened to allow the passage of larger vessels, it is called "the sea channel" ("Der Seekanal").