The managing director of Southern Water has resigned after four years in the role, it has been revealed.
The company said Stuart Derwent was leaving the firm immediately, having told staff he was quitting on Thursday.
A spokeswoman would not reveal the reasons for Mr Derwent leaving after 32 years with the water and sewerage firm.
Southern Water, based in Worthing, West Sussex, supplies water to about two million households in Kent, Sussex, Hampshire and the Isle of Wight.
The organisation employs about 2,000 staff and was bought in 2003 by French group Veolia, the Royal Bank of Scotland and other investors.
Southern Water said Bob Thian, who became chairman following the takeover, would assume some of Mr Derwent's responsibilities until a new managing director was found.
A spokeswoman for the trade union Unison, which has about 650 members among the water firm's staff, said: "There have been difficulties at Southern Water in the last 12 months and we have been working with the company and its staff to try to resolve them."