EVERETT — In an effort to protect a “once-in-a-lifetime opportunity,” the Everett City Council adopted an emergency six-month moratorium on any development at the Kimberly-Clark mill site.

The unanimous decision came without warning to the public late Wednesday night after an executive session.

Afterward, Mayor Ray Stephanson said the city wanted to keep a lid on the moratorium to keep any last-minute permits from being filed with the city.

“The development of our waterfront is a once-in-a-lifetime opportunity for Everett, and the city intends to ensure that it approaches future land-use decisions as well prepared as possible to make the best decision for the city’s future,” he said in prepared remarks.

City attorney Jim Iles told the council the measure was introduced to prevent “undesirable land uses” from cropping up at the mill site.

No one specified just what those undesirable land uses might be.

Kimberly-Clark was one of Everett’s largest employers, and most of the hundreds of people who worked there no longer do. The mill is expected to be fully closed by the end of March. Kimberly-Clark Corp. was in negotiations to sell its pulp and tissue mill on the waterfront to Atlas Holdings Inc. Those talks fell through in December because of environmental issues.

Since then, the mayor and other city officials have made clear they want to keep the 90 acres on the waterfront devoted to industry or a commercial enterprise that puts people to work.

The emergency moratorium covers the Kimberly-Clark site as well as several adjacent properties that the city collectively is calling the Central Waterfront Planning Area.

During the six-month period, the city plans to evaluate opportunities for future site use, said Allan Giffen, Everett’s Planning and Community Development director.

That conversation will include Kimberly Clark and other adjacent property owners, he said.

The moratorium has a few exceptions that will allow Kimberly-Clark to proceed with its plans to clean up the area and demolish buildings.

Giffen also said a public hearing on the matter should be scheduled in the next 60 days.