|Season 1, Episode 24|
|Japanese Title|| ウンディーネの湖|
|Episode 23: Don't Give Up, Ducken!||Episode 25: Warriors of the Ruins|
Undine's Lake is the twenty-fourth episode of Season 1 of the Monster Rancher anime series. It aired in Japan on October 2, 1999.
The Searchers come across a small, quiet lake in the forest. They decide to restock their food supplies with fish. However, the lake has another inhabitant, an Undine. Golem falls in love with the beautiful water spirit, but she turns out to be a servant of Moo. Will he be able to defeat her?
The Searchers arrive at a lake with no food, so they decide to fish. No such luck, as the only fish they catch is tangled up in Mocchi's line, (which causes Genki and the others to do the same thing like Mocchi did) and Suezo chomps it when nobody is looking (this cause Genki and the others to beat up Suezo). Hare has a plan to get them money for food: sell the oil from the nuts growing in the forest.
Golem makes a new friend from the lake that night, a water spirit, Undine. She wants Golem to stay, but he is on a journey, and promises to come back later. Undine tells Golem of a secret island available only at dawn where fish come to often. Golem tells them of the island, where they catch dozens of fish almost immediately. Tiger is suspicious, and he is right. It is all a trap, because Undine is actually working for Gray Wolf. She tries to destroy them with a whirlpool, but Mocchi fires his cannon to stop it.
While fighting Undine, Golem keeps defending her from Tiger's Torpedo attack. Everyone is confused by Golem's actions, even Undine. Golem says he knows what its like to be sad and alone. Undine tries to use Golem to her advantage but her plan backfires. She gets too close to Hare's oil and spills it, right on the fire. She is fatally burnt, and asks Golem and the Searchers for forgiveness, because of the way she took advantage of Golem's kindness. She turns into a Lost Disk.
- Unlike in the case of Naga, Undine's suicide was not edited out of the English version.
- Undine is seen at the end of Season 2 as one of the many Lost Discs to be restored.