How do you catch Feebas in Pokemon Sapphire?

No, Don't Worry we all want it to be that easy for Feebas (Feebas and Milotic are the only ones I need to complete my Hoenn Pokedex on Pokemon Emerald...).

You just have to be patient and keep fishing. Or you could use an action replay, but don't, it just makes the game boring.

Fish on every water tile three times with an old rod. You use the grid search. (first tile fish 3 times go to the next tile, fish three times, and so on.) Or if you meant throwing POKe BALLS, the easiest would be MASTER BALL, next is the NET BALL. But it is really easy to catch.

To catch a Feebas on Sapphire, I went to the river West of Fortree city, and, as above, fished in each grid in the river three times. If Feebas didn't appear, it wasn't a "lucky square", so move on. If it appears in a grid-square, then that will generate almost only Feebas', so fish it a LOT! I caught eight before leaving.

If you have Pokemon Heart Gold or Soul Silver as well as the Pokewalker, you can sometimes find Feebas in the Quiet Cave route. Of course, unlocking the route requires 100,000 watts (2 million total steps) to unlock, so you'll still need some patience.