I just beat Mars at Lake Verity in Platinum again, but before I battled her, I surfed to the cavern in the center of the lake. When I got there, I noticed that the puddles on the cavern floor looked like odd shapes, which got me wondering whether they actually mean anything or have anything to do with the lake trio or something.
Strangely-shaped pools of water appear in all three caverns below the three lakes of Sinnoh, where the player first encounters Uxie, Mesprit, and Azelf, known collectively as the lake trio. What the shapes of the puddles mean, if they mean anything at all, is unknown. Two circular, smaller puddles indicate where the other members of the trio are relative to the cavern, so that the two pools and the lake trio member make up a triangle, confirming each Pokémon's status as members of a group. However, battling Uxie and Azelf is considered battling in a cave rather than a puddle, despite both the player and the Pokémon standing in a puddle.
So, yeah, you can find the lake trio there, to my understanding. Of course, they don’t have any real meaning, but they are connected to the lake trio.
Hope this helps! :)
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