Finding shiny pokemon is simple always a 1/8192 chance, which a few things that are manipulated.
- In Silver there will be a Red Gyarados ( Shiny Gyarados ) at the Lake of Rage. It's kind of like an event almost, but is really nice.
- The " Masuda method " makes your chances for a shiny pokemon to appear 4/8192 in Gen IV and V. So if you're playing " Soul Silver " you could use this.
But for the most part, I think they basically threw that in there because the Shiny Gyarados is actually IN the Lake of Rage.
If you haven't caught it yet, sorry for the spoilers!