Poliwhirl

Evolution

Poliwhirl, the Tadpole Pokémon. Poliwhirl is a Water type Pokémon, and it evolves from Poliwag at level 25. Poliwhirl can evolve into either Poliwrath with a Water Stone, or Politoed by trading with a King’s Rock.

Red, Blue and Yellow

Poliwhirl was introduced in Red and Blue Version. It’s #61 in the Kanto and National Pokédex.
Poliwhirl can be caught by fishing in Routes 9 and 10 in Red and Blue. In Yellow, you can only catch Poliwhirl in Route 23 by fishing.
Poliwrath, a Water/ Fighting type, is the only evolution to Poliwhirl in Red, Blue and Yellow. Politoed wasn’t introduced until Gold and Silver.

Gold, Silver and Crystal

Poliwhirl in Gold and Silver got some new traits. There is now breeding, so Poliwhirl can either be male or female, and it’s in the Water 1 egg group. Poliwhirl can be evolved or caught Shiny as well. Poliwhirl can now evolve into Politoed, a Water type, by trading it with a King’s Rock attached.
Poliwhirl can be caught in Gold, Silver and Crystal on Routes 22, 28, 30, 31, 35, 44, Ecruteak City, Violet City, Mt. Silver and Viridian City by Surfing.

Ruby, Sapphire and Emerald

Poliwhirl cannot be caught in Ruby, Sapphire, or Emerald; you have to trade it from FireRed or LeafGreen. In Ruby and Sapphire, Pokémon got Abilities, and Poliwhirl’s is either Water Absorb or Damp. Water Absorb recovers 25% HP when Poliwhirl’s hit by a Water type move, and Damp prevents Exploding or Self Destructing in a battle.

FireRed and LeafGreen

Poliwhirl can be caught on Routes 6, 22, 23, 25, Four Island, Viridian City, Cape Brink, Cerulean Cave Floor 1 and Basement 1, Icefall Cave Entrance and Ruin Valley by fishing. You can then breed Poliwhirl and trade a Poliwag or Poliwhirl over to Ruby, Sapphire, and Emerald if you want.

Diamond, Pearl and Platinum

Poliwhirl can be caught in Diamond and Pearl on Routes 225, 227, and 228 by fishing with a Good Rod. Poliwhirl can be caught in Platinum on Routes 227 and 228 by Surfing. If you migrate a Poliwhirl from any of the Advance games, you’ll find Poliwhirl in the Pond area of the Pal Park.

HeartGold and SoulSilver

Poliwhirl can be caught on Routes 22, 28, 30, 31, Violet City, Ecruteak City, Mt. Silver, Viridian City, Cerulean Cave and the Safari Zone. In all of these locations, you can either fish or Surf to find Poliwhirl.
While not exactly in HeartGold and SoulSilver, you can catch Poliwhirl in your PokéWalker if you're strolling in the Sightseeing route.

Black and White

Poliwhirl can be caught on Route 6, Wellspring Cave, Challenger's Cave, Victory Road and the Giant Chasm, after beating the Elite Four and obtaining the National Dex. You can find Poliwhirl with a Super Rod, which is more rare, or in the rippling water spots.