Short answer. The owner of the nearer bank owns the entire island. Article 465 of the Civil Code provides that when a single island formed by alluvial deposits is more distant from one margin than from the other, the owner of the nearer margin is the sole owner of the whole island.
What the law says
If a single island thus formed be more distant from one margin than from the other, the owner of the nearer margin shall be the sole owner thereof.
Civil Code, Article 465 — Islands on Non-navigable Rivers. Read the full provision →
Three rules in one article
Article 465 handles three possible configurations for a newly formed island in a non-navigable, non-floatable river. If the island is closer to one bank, the owner of that bank gets the whole island. If the island sits in the middle of the river — equidistant from both banks — it is divided longitudinally in halves between the two bank owners. If parts of the island are nearer to different banks, those parts go to the respective nearest bank owners. The rule turns on proximity, not proportional frontage.
What kind of river this applies to
Article 465 applies only to rivers that are non-navigable and non-floatable. Navigable and floatable rivers are public property under Philippine law, and islands that form in them belong to the State, not to the owners of the banks. The distinction between public and private rivers therefore determines whether the bank owners have any claim to a newly formed island at all. If the river in question is navigable, the private ownership rules of Article 465 do not apply.
How the island must have formed
Article 465 specifically covers islands formed through successive accumulation of alluvial deposits — the gradual, natural buildup of sediment over time. This is called alluvion. The article does not cover artificial islands, artificially constructed landmass, or islands that existed before ownership of the surrounding banks was established. The formation must be a natural process, and the island must be new — created by the river's own movement and accumulation, not by human intervention or catastrophic geological change.
Practical implications for bank owners
If a new island has formed in a non-navigable river near your property, measure the distance from the island to each bank to determine whether it falls squarely on your side of the midpoint. If the island is closer to your land, you are the sole owner and may use it, fence it, or develop it consistent with applicable laws. If there is any dispute with the owner of the opposite bank about where the midline falls, or about whether the river is navigable, those are exactly the kinds of boundary questions a lawyer and a licensed surveyor should resolve before you make investments on the land.