Correct...just look around and you will find a thread pertaining to your question. But just a quick answer is Feebas is found at Route 119 where you must fish to obtain it, however Feebas is located in only six tiles of the whole river, and where the certain tiles are also depend on what your Trendy Phrase is in Dewford, though it isn't an indication of exactly what tile the Feebas will be in. My suggestion, if you really want Feebas, is to start at one end of the river and in each tile fish about 3 to 4 times making you way to the other side, and making sure you have fished every tile. Yes this may seem tedicious, which it is, but if you really want Feebas or Milotic then I guess it would be worth it.
Anywho, like I said, this has been answered many times before, so I'm just going to close this one.
*Closes