This one's an 80s cartoon series classic, following the adventures of the mythical Gummi Bears who live in the woods and protect the secret of magical gummiberry juice.
The season 3 half-episode "Water Way to Go" features a mermaid named Aquarianne, who crosses paths with the Gummi Bears Sunni and Gusto. Gusto is inspired to draw Aquarianne, who is initially flattered by the interest, but she is then kidnapped by the evil Igthorn who wants to use Aquarianne's sea beast guardian for his nefarious purposes. It's a brief episode by itself but the animation quality of Gummi Bears continues to astound decades on and Aquarianne is a lovely addition to the animated pantheon.
Many thanks to Abraham for telling me about this episode, and for also noting that Aquarianne has the same colouring (blonde hair and orange tail) as Madison from Splash, another property owned by Disney.