I had no idea there was a real whale that inspired the song.
According to the Huffington Post:

Kavna, the beluga whale that inspired the beloved children's song "Baby Beluga" by Raffi, passed away from a possible cancer-related illness on Monday afternoon at the Vancouver Aquarium.

The 46-year-old whale spent her life in captivity, according to the Vancouver Sun, but lived well beyond the life expectancy of her species. Aquarium workers told The Canadian Press that belugas typically live 25 to 30 years, and that Kavna may have been even older than her estimated age.