How do i catch water pokemon in pokemon leaf green?

to get the move surf you need to defeat a certain gym leader. for a fishing rod you can type in google pokemon leaf green walkthrough and it will tell you everything you need to know

You can catch a magikarp and then evolve it to gyarados. To do that, you must have a old rod at least. Go to Vermillion city, go to the house to the left of the pokemon center. When you enter the house, talk to the man sitting in a chair. He will say he is the fishing guru, and he will ask if you like to fish. To get the fishing rod, you must say yes. He will then say that u should become friends and will hand you the fishing rod. I hope that helped!