The river shifted and left new land behind: whose ground is it?

After more than a decade of drought, the same scene keeps repeating across the central valley and the south: the river that used to mark the boundary dropped, exposed a strip of stones and sand, and that strip has now been dry for years. Someone planted poplars. Someone moved the fence thirty metres. And someone, on the other side, is convinced that land belongs to them.

Chilean law does resolve the question, and it resolves it through Bello's Civil Code, which was already asking this same question in the nineteenth century. But the answer depends entirely on a distinction almost nobody draws: a river that drops in summer and rises again in winter is not the same thing as a river that has retreated for good. The first case creates no right at all. The second does.

The starting point: under article 30 of the Código de Aguas (the Water Code), the riverbed, or natural watercourse, is the ground the water "occupies and vacates alternately in its periodic rises and falls", and that ground is public property. As long as it remains a watercourse, it does not pass to neighbouring properties. What the law does allow the riverside owner to do is farm the part not covered by the water, and that is not the same as owning it.

When does land left by the river become mine?

This is called aluvión, or accretion, and is set out in article 649 of the Civil Code: it is the increase the riverbank gains from the slow and imperceptible retreat of the water. There are three requirements, and all three must be met:

• Slow. A sudden retreat over a single season does not count. It is a process measured in years.
• Imperceptible. Nobody can point to the day it happened, precisely because it was gradual.
• Permanent. This is the one that decides real cases. The water retreated and does not come back. If it returns every winter, there is no accretion.

When all three are met, the land passes to the owner of the riverside property by accession, one of the ways of acquiring ownership recognised under Chilean law. There is no need to buy it or apply for it: it is acquired by the mere fact of having occurred. The complication comes later, when it has to be proved and registered, and we get to that below.

What if the river only drops in summer and comes back in winter?

Then there is nothing to claim, and this is the mistake that causes the most conflict between neighbours. Article 650 of the Civil Code is explicit: ground the water occupies and vacates alternately in its periodic rises and falls forms part of the bank or the watercourse, and does not pass to the neighbouring properties.

Put another way: the strip that appears every January and disappears every July remains national public-use property, however many years you have been farming it. It can be cultivated, because the Código de Aguas itself allows that while the water is not occupying it, but farming it is not the same as possessing it as owner, and it does not turn into ownership with the passage of time.

The practical consequence is uncomfortable but worth knowing: moving the fence up to the water's edge in a dry year creates no right at all, and it can easily turn into a problem with the neighbour opposite, with the Dirección General de Aguas (the national water authority), or with both.

What happens if the river suddenly changes course?

That is a different scenario, with its own rule. Article 654 of the Civil Code governs a change of watercourse: when a river shifts course, riverside owners may carry out the works needed to return the water to its former course, but only with prior authorisation. And if the change of course leaves one of the banks dry, that land passes to the neighbouring owner under the rules of accretion.

It is worth stressing the authorisation point, because that is where people make costly mistakes. Works that alter a natural watercourse require authorisation, a requirement set out in articles 41 and 171 of the Código de Aguas. Moving stones with machinery to redirect the river, building levees or filling in the riverbed without a permit is an offence, and since Law 21.740 the DGA's fines run up to 2,000 UTM. We cover this in detail in our article on DGA fines and well regularisation.

How is an abandoned watercourse divided between the neighbours on both banks?

When the watercourse is abandoned entirely, the law does not award it to whoever got there first or fenced it off fastest. Article 655 of the Civil Code, written for a river that splits into two branches that never reunite, sets the test applied in these cases: an imaginary line is drawn lengthwise down the middle of the watercourse, and each half passes to the properties on the bank it belongs to.

If instead the river shifted towards only one bank, the land left exposed passes to the owners on that bank, who are the ones who benefit from the shift. Geometry decides, which is why this is a matter settled with a survey plan, not a conversation.

The four scenarios, in a table

What happened	Rule	Who owns the land
The water retreated slowly and permanently	Art. 649 Civil Code	Passes to the riverside owner by accretion
The river drops in summer and returns in winter	Art. 650 Civil Code and art. 30 Código de Aguas	Remains watercourse, national public-use property
The river changed course and left one bank dry	Art. 654 Civil Code	Passes to the neighbouring owner, under the rules of accretion
The watercourse was abandoned between two banks	Art. 655 Civil Code	Divided by a line down the middle of the watercourse

What if it happened the other way round and the water flooded my land?

The Civil Code also provided for that case, and it set a deadline. Under article 653, if a property is flooded and the water retreats within the following five years, the land reverts to its former owners. Once that period passes without the water retreating, the loss of ownership becomes permanent.

That five year deadline is one of the more surprising details, because it means simply waiting has a real legal cost. If your land was flooded, the date matters. We cover this from another angle in our guide on how to tell whether land sits in a flood zone.

The exception for rainwater ravines

Not every watercourse is public, and this exception settles a lot of farm disputes. Article 31 of the Código de Aguas extends the rules on public watercourses to intermittent streams, but carves out one case: natural watercourses of intermittent streams formed by rainwater belong to the owner of the property where they are found.

In other words, the ravine that only runs when it rains hard, and is a dry ditch through your land the rest of the year, is yours. A stream that flows year round, or one fed by snowmelt, is different. The owner does not decide this simply by looking at the land: it is the origin and pattern of that water that determines it, and a technical report is worth getting before claiming anything. A related issue, water running off a roof or draining from one property into another, is covered in rainwater between neighbours.

How is that land proved and registered?

This is where the real work lies, and it is the part people underestimate. Ownership by accession is acquired automatically by operation of law, but the Conservador de Bienes Raíces (the Chilean property registry) does not register facts, it registers title. Your current registration states an area and boundaries that no longer match the reality on the ground, and that gap has to be documented.

What is needed, in order:

• A georeferenced topographic survey of the property as it currently stands, fixing with coordinates where the water's edge is today and where the fence is.
• A comparison with the historical watercourse, backed by old survey plans, mapping, aerial photography or satellite imagery from different years. This is what proves the retreat was gradual and permanent, not a seasonal dip.
• A title search of the riverside properties, including the one on the opposite bank, because the mid-line can only be drawn once you know what each side is claiming.
• Registration regularisation, which normally takes the form of a correction to the recorded area and boundaries. We explain this step by step in how to change a property's recorded area and boundaries.

This is exactly the kind of case where having lawyers and surveyors on the same team changes the outcome, because the legal argument rests on the survey plan, and the plan has to be drawn up with the next step already in mind.

The costly mistake: moving the fence first and asking questions later

The temptation is obvious, and we see it often. The river dropped, the strip has been dry for four summers, the neighbour has not said anything, and moving the fence costs little. The problem shows up later, and it shows up in three different forms.

The first is the neighbour across the way, who one day puts up their own fence and finds yours fifty metres inside where they had calculated the mid-line to be. The second is the DGA, if works were carried out along the way that altered the watercourse without the authorisation required under articles 41 and 171. The third, and the quietest, is the sale: when a buyer turns up and their bank asks for the title search, the gap between the registered area and the actual surface halts the deal until it is regularised.

The right order is the reverse: first work out which rule applies, then draw up the survey plan and gather the evidence, and only then move the fence, backed by title that supports where it sits.

Frequently asked questions about land left behind by a river

Can I fence off the strip the river left on my bank?

It depends on whether the retreat was permanent or just a periodic drop. If the water comes back in winter, that ground remains watercourse and national public-use property, and fencing it does not create ownership. If the retreat was slow and permanent, the land passes to your property, but it is worth documenting that before fencing it, not after.

How many years does the watercourse have to be dry for it to become mine?

The law does not set a number of years for accretion. What it requires is that the retreat be slow, imperceptible and permanent, and that is proved with technical evidence comparing the watercourse across different periods, not with a fixed term. The only express deadline applies to the reverse case, the flooded property, where article 653 sets it at five years.

If the river shifted towards my neighbour's land, is all the exposed ground mine?

If the shift left the bank next to your property dry, that land passes to you under the rules of accretion. If instead the watercourse was abandoned between both banks, it is divided by an imaginary line drawn lengthwise down the middle, and each half goes to the property on its side. Which of the two cases applies to you is something the survey plan determines.

What if the river comes back after I have registered the land?

This is one of the reasons the initial classification matters so much. If the retreat was not permanent but part of a cycle, there was never any accretion, and the title is left exposed. That is why the evidence cannot rest on a single dry year: you need to show a sustained trend, and that is where imagery from different periods makes the difference.

Is the ravine that crosses my land mine?

If it is an intermittent stream formed by rainwater, article 31 of the Código de Aguas says that watercourse belongs to the property owner. If it is a permanent stream, or one fed by snowmelt, it does not: that is a public-use watercourse. The distinction is technical, and it is worth settling with a report before doing any work on the land.

Do I need a permit to move stones or level off the dry watercourse?

Works that alter a natural watercourse require authorisation under articles 41 and 171 of the Código de Aguas, and that includes work that seems minor on the ground. Doing it without a permit exposes you to DGA penalties, which currently run up to 2,000 UTM.

Land that appears, title that does not appear on its own

Prolonged drought has handed many riverside properties surface area they did not have before. In some cases that land already belongs to the riverside owner, and all that is missing is documenting it. In others it remains national public-use property, and occupying it is a risk. The difference between the two is not something you can see by looking at the land in August: it is established by comparing the watercourse over the years and setting that against what the title deeds on both banks say.

If your property borders a river or stream and the actual surface no longer matches the registered area, that mismatch is going to surface anyway the day you want to sell, mortgage or pass it on. It is worth sorting out calmly rather than discovering it mid-transaction. The procedures for watercourse changes and their requirements are described on the website of the Ministerio de Obras Públicas (the Public Works Ministry).

At Terreno en Regla we review the whole case before proposing a way forward: the title to your property, the historical watercourse, and the situation on the opposite bank. If the rule that applies does not work in your favour, we tell you upfront, because in these cases insisting on a fence in the wrong place always ends up costing more than the study would have.