"It’s long ears are indispensable sensors. By focusing its hearing, this Pokémon can identify what kinds of prey are around, even in rough and fast-running rivers."
Evolutions are sometimes meant to show just how much more powerful a Pokemon can become, and that's definitely the case with Azumarill. While Marill is cute, Azumarill is powerful, very powerful in fact. On land and in water, and as the Pokedex notes, its ears are more powerful too, so it can find you wherever you are just by hearing you.
Azumarill's Basic Attacks are Rock Smash and Bubble, while its Special Attacks are Hydro Pump, Play Rough, and Ice Beam.