Sheila Clark of Denver was with her 3-year-old daughter Isabelle last week visiting an area of the zoo called Amazon's Edge.
Clark said she was fidgeting with her wedding and engagement rings when they slipped from her finger.
"I pulled on it a little bit and they both shot off," Clark said. "One rolled that way and I caught it. The other rolled that way. I shot out to get it and latched onto thin air."
She managed to grab the wedding ring, but the other vanished into a moat filled with water.
The zoo director, Kent Yamaguchi, told her there was almost no chance they'd find it. But lucky for her, the zoo was draining the moat that week for repairs.
The director himself put on his rubber boots and fished around in the mud.
"All of a sudden I saw some gold shining out through the mud, just a little bit of the band," he said. I started screaming crazily, 'Yay! We got the ring!"
When she picked up the ring, she told the director she was heading to the beach. He suggested she might want to leave the ring at home.