Hippopotas locations — where to catch

In Lumiose City (Legends: Z-A)

• Wild Zone 7 — Walk

In Paldea (Scarlet & Violet)

• Asado Desert — Walk

In Hisui (Legends: Arceus)

• Celestica Trail — Walk
• Gapejaw Bog — Walk
• Scarlet Bog — Walk
• Sludge Mound — Walk

In Sinnoh (Diamond, Pearl & Platinum)

• Maniac Tunnel — Walk
• Ruin Maniac Cave — Walk

In Johto & Kanto (HeartGold & SoulSilver)

• Johto Safari Zone — Walk

Other games (4)

• Brilliant Diamond / Shining Pearl (Gen 8): Maniac Tunnel
• Sword / Shield (Gen 8): Dusty Bowl, Route 6, Galar Route 6
• X / Y (Gen 6): Kalos Route 9
• Black / White (Gen 5): Route 4

Hippopotas — full Pokédex entry