The emergency services were looking for a man seen entering the River Lagan in Belfast today.
At 3.11am, the fire service received a report that a person had gone into the water at Queens Bridge.
Police, the Coastguard and the RNLI were involved in the search.
Meanwhile, a man was rescued from the River Foyle in Derry this morning. A rope and lifebuoy were thrown to him.
He was taken to hospital but was not expected to suffer any lasting ill-effects.