Fishing has been a major element of Pokémon since the original games, and always had you fishing wherever there was water in order to hook various Pokémon. Pokémon Sun & Moon changes that. Rather than fishing everywhere, there are specific spots in various places, denoted by a combination of rocks with a hole in the middle, where you can fish. These can be coastline or out at sea when surfing on Lapras.

Each rock has got its own encounter table and so different Pokémon may appear at different ones in the area. There is also only one Fishing Rod

The following locations can be fished in: Route 7, Route 8, Route 9, Route 13, Route 14, Route 15, Akala Outskirts, Brooklet Hill, Kala'e Bay, Melemele Sea, Paniola Town, Poni Breaker Coast, Poni Gauntlet, Poni Meadow, Poni Wilds, Seafolk Village, Seaward Cave, Secluded Shore, Vast Poni Canyon

There are a few more elements to fishing. In each area, you will sometimes see the fishing spot bubble. If you approach this spot, you can fish in it and you'll get a different encounter table, typically making the rarer Pokémon such as Dratini, Corsola or Feebas be more common. However, if you move too fast around it, the area will disipate and will require you to re-enter the route to access it

Items are also a thing that can be hooked when fishing. When you get something on your hook, there is slim chance that you instead hook an item such as Pearls, Pearlstrings or even Bottle Caps.