The Denver Zoo's harbor seal, Kim. 

The Denver Zoo’s 33-year-old harbor seal was put down last week after suffering a significant health decline, the zoo announced Monday.

The seal, named Kim, lived in the zoo for her entire life. She was known for enjoying live fish and taking naps in the pool skimmers where the bubbles came out, zoo officials said.

“Kim was a sweet, smart and spunky seal who was a beloved member of Denver Zoo,” the zoo said in a statement. “She will be dearly missed by keepers, staff, volunteers and guests.”

Kim’s appetite and activity levels had drastically declined over the past several weeks, though vets could not determine a cause, the zoo said. Attempted treatment of Kim's symptoms were ineffective, leading to her euthanasia, officials said.

At 33, Kim surpassed the average life expectancy for her species. Harbor seals typically live 15 to 20 years in the wild and 25 to 30 years in captivity, according to the zoo.

Kim was the only harbor seal at the Denver Zoo, a spokesperson for the zoo said. She lived with the zoo’s group of sea lions.

“Even in a barn full of sea lions, Kim most definitely held her own and showed those sea lions who’s boss,” the zoo said in a statement.

The spokesperson said the zoo does not have plans to replace Kim with another harbor seal.

Harbor seals, also known as the common seal, are found along coastal regions and near islands of the northern Atlantic and the northern Pacific oceans.