Shedd Aquarium Euthanizes Rio, 21-Year-Old River Otter (PHOTOS)

The Shedd Aquarium has bid a sad goodbye to its 21 year-old North American river otter, Rio.

In a blog post Tuesday, aquarium officials said both its animal care and animal health teams made the "difficult but humane decision" to euthanize Rio after her health and quality of life recently went on the decline.

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Rio, who was exactly 21 ½, lived an exceptionally long live given the average lifespan of a river otter is about 12 years.

The aquarium recounted the charismatic otter's life as a popular fixture at the Shedd:

Rio had many fans who would wait expectantly at the windows of her habitat for her to bound out of her cave, scamper along the rockwork and dive into the water where she’d twirl and zoom before leaping out and doing it again. She made good use of her extra-large habitat in the At Home on the Great Lakes gallery, enabling everyone along the windows to see her. After her romp, she’d retire to her cave again for a catnap before the next round of playful activity. She also enjoyed her twice-daily training and enrichment sessions, which included batting around her favorite food-stuffed toys.

Ken Ramirez, executive vice president of animal care and training, said in a news release Rio's long life became a testament to the zoological community’s emerging expertise in geriatric animal care and welfare."

Rio first came to the Shedd from the Little Rock Zoo in Arkansas in 1992 as a "high-spirited, adventurous pup."

(Read more about Rio's life at Shedd Aquarium.)

ABC Chicago notes that when Rio arrived in Chicago more than two decades ago, river otters were on the endangered species list in Illinois, though that has no longer been the case since 2004.

Godspeed, Rio!