"The Missing Fast-Water Adventure" is the fourteenth episode of the animated children's series The Land Before Time. It originally aired on April 20, 2007.
The episode starts with the gang playing in a pond. An earthquake starts and causes the rocks to block the water flow in the river. The whole dinosaurs in the Great Valley discusses the grave news but everyone disagrees with Littlefoot's idea of bringing the water back. The gang decides to find the source of the empty water flow. They find that rocks are blocking the water and doesn't risk of drowning. Ducky volunteers to see how deep the water is. The others find a shadow in the water that isn't Ducky and fears it is a swimming sharptooth.
Ducky manages to get out of the water and the figure in the water turns out to be Mo, an old friend from The Land Before Time IX: Journey to Big Water when after firing water at Littlefoot, Spike and Cera. Mo makes his greeting to his old and new friends. Turns out that Mo was looking for Littlefoot after he saw the land and water connected. The gang decides to clear a bit of rocks and not all of it to get enough water flowing.
Chomper tries to help but he ends up almost drowning but is saved by Littlefoot, Mo, Ducky and Ruby. After pushing off some rocks, more rocks fall and blocks the river even more. Apparently, Spike discovers that there is a log connecting to both sides of the rocks and a rock is blocking it. The figure out that by moving the rock, the water will flow again. Ruby tries to get it, but the rock proves to be far away.
Chomper sees that his tiny arms are small enough to go into the small hole and pulls out the vine holding the rock and the water continues to flow once more. Now the gang and Mo must part ways but even if they're far away, they will always be friends. The Great Valley is having its water again. Mr. Threehorn apologizes to Littlefoot and Chomper and everyone celebrates the return of the water.
- Cody Arens as Littlefoot
- Anndi McAfee as Cera
- Aria Noelle Curzon as Ducky
- Jeff Bennett as Petrie
- Rob Paulsen as Spike/Mo
- Max Burkholder as Chomper
- Meghan Strange as Ruby
- John Ingle as Topsy
- Kenneth Mars as Grandpa Longneck
- Kosh appears but has no lines.
- Mo makes another appearance in this episode. He calls Littlefoot and all his friends his "mud brothers." Mo also gets to meet Chomper and Ruby for the first time.
- Grandpa Longneck mentions the time all the water dried up in Time of the Great Giving.
- Ducky notes that Ruby has the longest arms than the rest of the group, whilst Chomper has the shortest arms.
- After being saved from drowning, when Chomper exclaims "I guess I wasn't much help after all," the top of his upper jaw, surrounding his nose, is grey instead of purple.