One of the Philadelphia Zoo's two polar bears was euthanized Friday morning after efforts to treat her serious health issues failed.

The zoo said Klondike, who was nearly 35 years old and had been a favorite for visitors and keepers alike since she arrived in Philadelphia in October 1981, had experienced deteriorating health over the past two weeks, including difficulty standing and walking.

She showed no improvement after treatment for a urinary tract infection and the mobility issues, the zoo said. Caretakers decided to euthanize the bear due to her advanced age and poor prognosis for returning to a good quality of life.

Klondike, who had been the oldest polar bear in the country, will be "greatly missed," general curator Kevin Murphy said in a statement.

"In addition to the joy she brought guests over more than three decades, she has been an important ambassador to wild polar bears, who are increasingly threatened by climate change and resulting shrinkage of polar ice," he said.

Klondike was born at the Bronx Zoo in November 1980.

The Philadelphia Zoo has one remaining polar bear, 34-year-old Coldilocks, who is now the oldest in the nation. Polar bears in zoos typically live to about 24 years of age.