How do I own a land given by nature legally?

[Vistabel]

This land it was a portion of a big river before then the river itself left that portion and changed its path of waterways to another location, the area of previous river it is now a very fertile land for farming probably class "A" type soil it has and that land which I prefer to own legally because there are many people also interested to have a part of that land area. I think using gun to have this land is not advisable.

Gusto sab unta nako'ng patitulohan kining mga gagmay isla nga walay taw diri sa amoa, pwede kaha?