In Pokémon games, these hedges, rocks, and bodies of water usually hide new secrets and routes; you typically unlock them by completing a certain area or defeating a Gym Leader. However, since the game is still in development, it seems those options aren't available yet.
For the hedges, you need to learn the Cut move with a Pokémon.
For the rocks, you need the Break move to break them and the Push move to push them—both are Pokémon moves as well.
For the water, you need to learn the Surf move with a Water-type Pokémon.
Translated with DeepL.com (free version)