State regulators have approved the Boston Harbor Hotel’s plans to convert a ninth-floor observatory that’s been open to the public since 1985 into private guest space.

Pyramid Hotel Group, owners of the property, closed the observatory’s balcony after an apparent suicide several years ago. In February, they sought permission to permanently close the 1,458-square-foot indoor observatory located beneath the central rotunda.

In exchange, Pyramid will convert a 1,750-square-foot office on the ground floor into a free visitors’ center, meeting room and public restrooms open seven days a week.

The observatory had been open to the public under the hotel’s waterways license, required under state Chapter 91 regulations for waterfront properties. In a decision issued Nov. 26, the Department of Environmental Protection approved the hotel’s request.

The conversion was supported by nine stakeholders including the Boston Harbor Alliance, New England Aquarium and Boston Mayor Martin Walsh.

Pyramid said the observatory attracted no more than 150 people a year, but opponents blamed its lack of popularity on inadequate signs and public notice. In response to a request from the Boston Redevelopment Authority, the hotel has agreed to host quarterly architectural tours of the rotunda.

The decision can be appealed by Dec. 17, according to DEP spokesman Edmund Colletta.