An ice runway in New Hampshire will remain closed this winter because mild weather has made the ice unsafe.

The ice isn't thick enough at the Alton Bay Seaplane Base ice runway to support maintenance vehicles and aircraft, runway manager Paul LaRochelle told New Hampshire Public Radio.

No full-scale vehicles should cross the lake this season, and anyone snowmobiling should exercise caution, LaRochelle said.

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“It takes more than a few cold nights," LaRochelle said. “It takes weeks for it to be a good thick safe ice."

In this Feb. 28, 2015, file photo, planes are parked after landing on a frozen Lake Winnipesaukee in Alton, N.H. (AP Photo/Jim Cole,)

The seasonal runway on Lake Winnipesaukee is the only ice runway in the lower 48 states approved by the Federal Aviation Administration.

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LaRochelle said he doesn't think the closures are indicative of a long-term trend. The runway was also closed in 2016 and 2011.