At two strain-sensitive wells located close (~5 km) to seismic swarm activities off the Izu Peninsula, Japan, we observed water-level changes that were synchronized with bursts of seismic activity during an active period in October 1996. The water levels started to drop at the onset of each burst, and stopped dropping as it ceased. This is the first hydrological observation in response to bursts in this area. The data suggests the occurrence of some local crustal deformation at the time of the bursts of seismicity. ¿ 1999 American Geophysical Union