The melting snow and ice is winding down one of this winter’s most beautiful phenomena.

The wildly popular mainland ice caves at the Apostle Islands National Lakeshore will be closing no later than Sunday night, park officials announced Wednesday, due to “rapidly changing ice conditions and growing day-to-day uncertainty about safety.”

Officials will continue to monitor ice conditions before then, and if the ice weakens too much they warned they could shut down access sooner. Seeing the caves requires walking atop frozen Lake Superior; the last time that was possible was in 2009.

Park Superintendent Bob Krumenaker called this winter the longest and best ice cave season that anyone can remember. Since word spread on social media that the caves were open starting Jan. 15, about 125,000 people have visited, pumping an estimated $10 million to $12 million into the local economy. The previous record for winter visitors to the caves was 12,000. The entire park drew 150,000 visitors in all of 2013.

“But spring is coming, the ice is weakening, and we can see the edge of the ice pack coming closer to the mainland ice caves every day,” Krumenaker said in the news release. “The beautiful formations are melting and some have already fallen, raising concerns.”

Safety is the top priority and planning a closure rather than reacting to changing conditions will assure the season ends on a high note, the release said.

“Nobody wants something really bad to happen,” Krumenaker said in an interview. “It’s obvious the ice is degrading … closing it before something happens is much better than waiting a little bit too long.”

Those still hoping to visit the caves should call an automated ice line at 715-779-3398, extension 3, for conditions.