Cheryl Taylor, the city's commissioner of public works and environmental quality, resigned abruptly earlier this week.
City spokeswoman Susan Straub released a statement on Thursday saying, "We wish the situation were different. We wish her well." Straub declined to comment further.
Attempts to reach Taylor for comment were unsuccessful.
Susan Bush, director of the Division of Environmental Policy, will serve as interim commissioner until a permanent replacement can be found.
Taylor, 54, was Lexington's first environmental quality commissioner, named to the post by former Mayor Jim Newberry in November 2007. A major part of her job was overseeing city efforts to comply with a February 2008 settlement with the U.S. Environmental Protection Agency that requires Lexington to pay up to $300 million over the next decade to repair sanitary and storm sewer systems that have polluted creeks.
In 2010, Taylor left the city post to take a job with Kentucky American Water as manager of production.
Newberry said in a statement then, announcing Taylor's departure, that in less than 21/2 years Taylor had established environmental protections that were new to Lexington and "laid the groundwork for ensuring that we will be able to leave our environment in better condition than we found it."
Taylor was among Mayor Jim Gray's first nominees for commissioners.
Before coming to work for Lexington, Taylor was Kentucky's environmental protection commissioner. Prior to that, she was an engineering manager for Procter & Gamble.