Navy Pier closed its climate-controlled Ferris wheel Sunday and Monday for the “well-being” of its staff as the city experiences near-zero temperatures.

The heated gondolas spin year-round, but when temperatures near Lake Michigan drop too low Navy Pier must shut down operations, a spokesperson said.

“For the safety of our guests and staff, the Centennial Wheel must occasionally close due to weather conditions, such as lightning, high winds and extreme cold,” spokesperson¬†Payal Patel said. “Today, the closure is due to the below-zero temperature near the lake. This measure is taken primarily for the well-being of our guests and staff who work outside in the extreme cold.

The Ferris wheel has been shut down for part of at least 15 days so far this winter for wind or freezing temperatures, according to Navy Pier’s Twitter account.

The Ferris wheel started operating in May 2016, replacing a smaller Ferris wheel that operated for 2o years.