Route 124, 125, 126, 127, 128, 129, 130, 131, 132, 133 and 134 in Hoenn.
I know it's basically a meme at this point, but Hoenn really does have too much water. The part of the game between Lilycove and the elite 4 has got to be my least favourite part in any Pokémon game because of how boring water routes are, and forces you to either use a HM slave for a large portion of the game, or put two water HMs on your water type.
