A firefighter in a waterproof suit crossed a partially frozen Arizona lake to help rescue two teenagers who had spent at least two frigid hours hanging onto a dead tree after ice began to crack, authorities said Thursday.

A third teen who had stayed on the bank of Fool Hollow Lake, near Show Low, called for help Wednesday, while the other two clung to the tree, authorities said.

Emergency personnel retrieved the boys after firefighter Jack Gessner made his way across the lake with a rope attached to a boat.

Gessner said he initially crawled atop the ice, then had to swim through the water after the ice broke. His suit and training worked as designed, leaving him dry but tired.

‘‘I thought it went well,’’ said Gessner, a firefighter on the ice rescue team of Lakeside Fire District. “It was a really good team effort and everybody did their jobs.’’

Gessner said the boys did not seem to be panicking and were OK as he swam by the tree to reach the shore and get a foothold to hold the rope.

The boys were taken to a hospital for treatment of mild hypothermia.