TACOMA, Wash. — A 19-year-old southern sea otter known for her ability to stack plastic cups has died at the zoo where she lived in Washington state.

Officials with the Point Defiance Zoo and Aquarium in Tacoma said Tuesday that Nellie was euthanized Sunday after experiencing an acute illness.

A zoo spokeswoman says veterinarians will have a better idea of the cause and nature of the illness once they get test results.

Nellie learned to use her forepaws to stack the nesting cups before she came to the Tacoma zoo in 2004. Tacoma keepers continued to do it with the otter as a way to help keep her physically active and mentally alert.

A zoo video of Nellie posted on YouTube three years ago has been viewed more than 2.6 million times.