It's not goodbye...it's seal you later.

The Denver Zoo is mourning the loss of its longtime resident Kim, a 33-year-old harbor seal who kept visitors educated and entertained for years.

According to a Facebook post, the zoo made the difficult decision to humanely euthanize Kim last week after she exhibited low activity levels and a loss of appetite. Despite attempts to treat her symptoms, she continued to experience "a significant decline in her health."

The zoo's veterinarians were unable to determine Kim's cause of death; however, she exceeded the harbor seal's typical life expectancy — the animals live 15 to 20 years in the wild and 25 to 30 years in captivity.

"Even in a barn full of sea lions, Kim most definitely held her own and showed those sea lions who's boss," read the post. "According to her keepers, Kim loved live fish enrichment, puzzle feeders and taking naps in the pool skimmers where the bubbles came out."

The zoo frequently showcased Kim's skills, including how she "fished" for food, on social media. On her birthday, keepers would allow Kim to enjoy the Northern Shores exhibit by herself — without her noisy sea lion roommates.

While the Northern Shores exhibit won't be the same without Kim, guests can still stop by to see the zoo's six sea lions: Nick, Duke, Maverick, Luci, Ady, and Gunnison.

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

Animals of the Denver Zoo