Water discharge fluctuations in ungauged rivers, especially in the face of climate change and urban sprawl, can be dangerous and destructive. The water discharge dynamics of small urban rivers are highly variable and complex. Understanding these dynamics and their underlying causes is necessary for public awareness. Our work is focused on the small ungauged river Lipovka (Lipetsk, Russia). It has a 50.1 km2 urbanized watershed with an outlet in Komsomolsky Pond in Lipetsk’s city center. We used several independent methods to study the hydrological regime of the Lipovka River. Based on in-situ measurements in spring 2022, we estimate the water discharge with a 1% annual exceedance probability according to the regulatory document SP 33-101-2003. Furthermore, we used data from the Lipetsk meteostation to run a Hydrologiska Byråns Vattenbalansavdelning model (HBV) to simulate a daily hydrograph for the 2005–2022 period. We found that the reduced runoff of the Lipovka River was mainly caused by a decline in the effective catchment area, a littered channel, and increased evaporation and filtration into the groundwater. To reestablish the river's natural flow and catchment area, we propose constructing and maintaining a culvert to enable upstream feeding of the Lipovka River by Syrsky Pond. In the context of smart urbanization, our study can be used to design and revitalize small urban rivers that form a crucial component of a city's water-green framework. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.