Can You Own the Seabed? Understanding Private Ownership Rights of Underwater Land in Japan

The question of whether individuals or private entities can hold ownership rights over land submerged beneath the sea is a complex one, with answers varying significantly across legal systems. In Japan, a country with an extensive coastline and a deep historical relationship with the sea, the legal framework governing the ownership and registration of seabed (kaimenka no tochi, 海面下の土地) is nuanced, shaped by longstanding administrative practices, key governmental directives, and judicial interpretations. While the general principle leans against private ownership of the natural seabed, specific circumstances and legal processes can alter this position.

The General Starting Point: Seabed as Public Domain and the Registration Boundary

Traditionally, Japanese legal understanding, reinforced by early judicial precedents such as a 1915 (Taisho 4) decision by the Great Court of Cassation (Taishin-in, 大審院), has considered the seabed in its natural state to be part of the public domain and thus not ordinarily subject to private ownership in the same way as terrestrial land. For land to be registered in the Japanese Real Property Registry, it must typically be a defined parcel capable of exclusive control and use.

The physical boundary determining what constitutes registrable "land" as opposed to "sea" was clarified by a pivotal Ministry of Justice Civil Affairs Bureau reply on November 10, 1956 (Showa 31). This directive established that for tidal waters, the boundary is the high tide mark during the spring and autumn equinoxes (春分秋分における満潮位 - shunbun shūbun ni okeru manchōi). Land lying below this specific high tide line at these times is generally considered part of the sea and not registrable as private property.

Submergence of Registered Land: The 1958 (Showa 33) Chiba Port Directive

What happens if land that was once dry and duly registered as private property subsequently becomes submerged? A notification from the Civil Affairs Bureau, issued on April 11, 1958 (Showa 33, Minji San No. 203), addressed such a scenario in Chiba, in the context of a port construction and land reclamation project.

The Scenario: The project involved areas where land, previously registered as privately owned, was found to be consistently submerged below the spring/autumn equinoctial high tide line.

Key Findings of the 1958 Notification:

1. Loss of Private Ownership Character: The notification reaffirmed the principle that private ownership rights are generally not recognized over land that is, in its current state, submerged below the defined equinoctial high tide mark. Its physical transformation into seabed fundamentally alters its capacity to be treated as ordinary private land for registration purposes.
2. Owner's Duty and Registrar's Authority for Display Registrations:
   • The registered owner of such submerged land has a duty to apply for a registration of land extinction (tochi messhitsu tōki, 土地滅失登記) or, if only a portion is submerged, a registration to correct the land area (chiseki kōsei tōki, 地積更正登記) to reflect its diminished terrestrial extent.
   • Crucially, if the owner fails to make such an application, the registry office is not powerless. If the fact of submergence and its extent can be reliably confirmed (for example, through official notification from a public project implementer like the Chiba Port Construction Office in this case), the registrar has the authority to make ex officio (職権 - shokken) amendments to the Land Ledger (tochi daichō, 土地台帳 – an older land record system that was being integrated with the formal property registry, or tōkibo, 登記簿).
   • Regarding the formal property register, the 1958 notification implied that if the owner of the submerged (but still registered) land did not apply for its extinction, and the area was subsequently lawfully reclaimed by another party (e.g., the port authority), the reclaimer could proceed to apply for a new ownership preservation registration (shoyūken hozon tōki, 所有権保存登記) for the newly created land. This effectively allows the new registration reflecting the reclaimed state to supersede the now-defunct registration of the formerly private, now permanently submerged, land.

This 1958 directive underscored that the current, verifiable physical state of the land is paramount in determining its ongoing registrability as private property.

Nuances of Submergence: The 1961 (Showa 36) Ministry of Finance Airbase Directive

Further clarifications came with a Ministry of Justice Civil Affairs Bureau reply on November 9, 1961 (Showa 36, Minji Kō No. 2801), in response to an inquiry from the Ministry of Finance concerning former naval airbase lands. This case involved more complex scenarios:

• Area A: Land that was already seabed (1 to 8 meters deep) when it was acquired by the former Navy Ministry. Although this area appeared on old cadastral maps and land ledger maps with lot numbers (and was re-categorized as "miscellaneous land" upon acquisition), its status as seabed at the point of state acquisition meant that ordinary property ownership (by the state, in this instance, as transferable property) was not recognized.
• Area B: Land that was originally reclaimed dry land (used for paddy fields, housing, etc.) but became seabed after its acquisition by the Navy. This change occurred because a dyke was partially removed to facilitate seaplane operations, allowing seawater to inundate the area. While this area was shallow, with old dyke remnants visible at low tide, and its restoration to dry land was considered "not difficult," its then-current state as seabed led to the same conclusion: ordinary property ownership was not recognized.

The Critical Exception: Temporary Submergence by Natural Disaster
The 1961 reply introduced a very important distinction and exception:

• If land becomes submerged as a direct result of a natural disaster (tensai tō, 天災等 – e.g., earthquake-induced subsidence, tsunami effects, major flood), AND this submerged state is deemed to be "temporary" (ichijiteki na mono, 一時的なもの), then pre-existing private ownership rights over that land do not automatically extinguish.

Interpreting "Temporary" and the Implications for Area B:
The concept of "temporary" is crucial. It implies a reasonable expectation that the land will either naturally re-emerge or can be restored to its former state without extraordinary or economically unfeasible efforts. This is a factual determination to be made by the registrar, likely based on surveys and assessments.

In the case of Area B, although its restoration was deemed "not difficult," the submergence was due to deliberate human action (dyke removal for operational purposes) rather than a natural disaster. Furthermore, its condition was not presented as a temporary state pending natural recovery or immediate planned restoration. Therefore, despite its prior existence as dry land, its current, non-temporary (and non-natural-disaster-induced) seabed status meant it lost its character as privately ownable/registrable land. This suggests that if land becomes seabed through human actions that are not part of a formal reclamation process converting sea to land, it may be treated similarly to land permanently lost to the sea through natural, non-temporary causes.

Synthesizing the Principles of Seabed Ownership and Registration

From these administrative directives and broader legal principles, several key points emerge regarding the private ownership and registration of underwater land in Japan, particularly seabed:

1. Primacy of Current Physical State: For a parcel to be (or remain) registered as private land, its current physical state must generally be that of terrestrial land, existing above the legally defined sea boundary (the high tide mark at the spring/autumn equinoxes).
2. Permanent/Non-Temporary Submergence Leads to Loss of "Land" Character: If a registered parcel of land becomes permanently or non-temporarily submerged below this line, it generally loses its characteristics as registrable private "land." The original owner is expected to apply for an extinction registration.
3. The Narrow "Temporary Natural Disaster" Exception: The primary recognized exception allowing for the retention of private ownership over submerged land is when the submergence is a direct consequence of a natural disaster and the condition is verifiably temporary, with a realistic prospect of restoration.
4. Human Actions Leading to Submergence: If private land becomes seabed due to deliberate human intervention that is not part of a lawful reclamation project (as seen in the 1961 airbase case with the dyke removal), it also appears to lose its status as registrable private land.
5. Judicial Perspectives on Submerged Private Land: It's worth noting a 1986 (Showa 61) Supreme Court decision which indicated that if already private and registered land becomes submerged due to natural causes, the underlying private ownership right itself does not automatically extinguish, provided the land remains identifiable and potentially susceptible to some form of control or use. This introduces a potential nuance: while the registry office, following administrative guidelines, might determine that currently submerged land does not meet the physical criteria for ongoing "land" registration (a hyōji or display matter), the substantive ownership right might not be entirely lost in the eyes of the court, especially if restoration is feasible. However, for the practical purposes of initial registration or maintaining an existing registration's status as "land," the administrative precedents focusing on the land being physically above the equinoctial high tide mark are generally paramount for registrars.
6. The Path to New Private Land from the Sea: Reclamation: The most common and legally straightforward way for an area of seabed to become private, registrable land is through lawful reclamation (umetate, 埋立) conducted under the Public Waters Reclamation Act. Upon completion and official approval of such a project, new land is legally created, and ownership typically vests in the entity that undertook the reclamation. This new land is then subject to a new land registration.

Distinguishing Seabed from Other Underwater Areas

It is also important to remember that the principles discussed here primarily concern kaimenka no tochi (seabed land). The rules governing the ownership and registration of land beneath inland waters, such as riverbeds (kasenshiki, 河川敷) or lakebeds, can differ and are often subject to distinct laws (e.g., the River Act - Kasenhō, 河川法) and local regulations or customs.

Conclusion: A Framework for a Fluid Boundary

The question of private ownership and registration of seabed in Japan is governed by a framework that prioritizes the current physical state of the area in relation to a specifically defined tidal benchmark – the high tide mark at the spring and autumn equinoxes. While the default position is that the natural seabed is public domain and not subject to private ownership, exceptions exist. The most significant is for land that becomes submerged temporarily due to a natural disaster.

For practical purposes, the transformation of seabed into new, privately registrable land is overwhelmingly achieved through formal, legally sanctioned reclamation projects. The administrative directives from 1958 and 1961 remain vital in guiding registry office practice, ensuring that the land register accurately reflects the physical reality of what constitutes controllable, usable, and therefore privately ownable land at the sea's edge. These rules provide a degree of certainty in a naturally dynamic environment.