The HSE has says elective inpatient, day case surgery and endoscopy appointments planned to take place this week at Letterkenny General Hospital will be rescheduled.
It follows the extensive flooding on Friday which forced the emergency department to close.
Heavy rain caused a stream at the back of the hospital to overflow its banks and up to a metre of water gushed through the doors of the emergency unit .
A major clean-up operation is continuing and the HSE said a Contingency Management Team is in place to give regular updates on an ongoing basis.
Emergency admissions will continue to be diverted to Sligo Hospital and Altnagelvin in Derry with ambulance support in place.
Some clinics and services have been relocated to other hospitals in the county and the HSE said all patients concerned are being contacted individually.
The hospital is also closed to visitors.