Environment Agency boss Sir Philip Dilley has quit following the furore over this winter's floods.
Dilley, who received a grilling in front of MPs last week, said he was "disappointed" that he was having to tender his resignation, insisting he was "well qualified to carry out this role, and had much to contribute".
However, he added: "The expectations of the role have expanded to require the chairman to be available at short notice throughout the year, irrespective of routine arrangements for deputy and executive cover.
"In my view this is inappropriate in a part-time non-executive position, and this is something I am unable to deliver."
He added that media scrutiny was "diverting attention from the real issue of helping those whose homes and businesses have flooded, as well as the important matter of delivering a long-term flood defence strategy".
"This same media attention has also affected and intruded on my immediate family, which I find unacceptable," he added.
Dilley has come under increasing pressure to leave after it emerged he was on holiday while parts of Britain battled severe flooding. He faced intense criticism for failing to come home from his Caribbean trip, with the Environment Agency issuing a statement saying he was "at home with his family".
Yesterday it was reported that claims made by his office that his wife was from Barbados were false - June Dilley is actually from Jamaica, some 1,200 miles away.
Dilley insisted he had "not made any untrue or misleading statements, apart from approving the statement about my location over Christmas that in hindsight could have been clearer".
Environment secretary Elizabeth Truss thanked him for his work during "some challenging times".
The current deputy chairman, Emma Howard Boyd, is moving to become acting chairman with immediate effect, while the government begins the task of recruiting a permanent replacement in due course.