Why Are Hippos Swimming by the Sea?

Introduction

The Bijagós Archipelago is one of the few places on Earth where an animal usually associated with rivers and lakes can sometimes be seen moving through tidal channels and even swimming in coastal waters. The hippos of Orango National Park have become one of Guinea-Bissau’s most famous wildlife stories, often described as “saltwater hippos”. That description sounds almost mythical, but the underlying phenomenon is real: these are ordinary common hippopotamuses that have adapted their behaviour to an unusual island landscape of mangroves, lagoons and shifting tides rather than becoming a separate species. At the same time, the islands themselves are bound together by sacred traditions that have helped protect habitats and wildlife for generations, creating an unusual meeting point between ecological science and living belief.[unesco.org]whc.unesco.orgUNESCO World Heritage CentreCoastal and Marine Ecosystems of the Bijagós Archipelago17 Jul 2025 — The site is home to a rich biodiversity…

Why are hippos swimming by the sea?

The heart of the story lies on Orango and neighbouring islands in the Bijagós Archipelago. Unlike most hippos, which spend their days in permanent rivers or lakes, the Orango population regularly travels through mangrove creeks, tidal flats and coastal lagoons influenced by the Atlantic Ocean. During some seasons they may even be seen crossing stretches of shallow coastal water between feeding areas.

This has led to repeated descriptions of them as “marine” or “saltwater” hippos. The phrase is colourful but can also be misleading. Zoologists do not regard them as a distinct species or recognised subspecies. Instead, they are a geographically isolated population of the common hippopotamus whose behaviour has adapted to an island environment where freshwater, brackish water and seawater are closely connected by the tides. Their movements appear to follow seasonal changes in water levels and food availability rather than any mysterious attraction to the sea itself.[fundacion-biodiversidad.es]fundacion-biodiversidad.esFundación BiodiversidadImproving the food security of the Bijago population and…The project aims to resolve conflicts between rice cro…

From a Fortean perspective, the spectacle is memorable because it overturns expectations. Hippos are almost universally imagined as inhabitants of inland African rivers. Seeing them emerge from mangroves beside Atlantic beaches feels almost surreal, encouraging travellers to describe them as impossible or legendary even though careful ecological research explains how they survive there.

The Orango hippo oddity

The Orango population is scientifically significant for several reasons beyond its unusual habitat.

First, it occupies the western edge of the species’ natural range. Isolation on the islands has created a relatively small and vulnerable population whose conservation is treated as a priority in international hippo action plans. Local conservation projects have also had to balance protection of the animals with the needs of island communities, particularly where hippos raid rice fields.[Fundación Biodiversidad]fundacion-biodiversidad.esFundación BiodiversidadImproving the food security of the Bijago population and…The project aims to resolve conflicts between rice cro…

Second, their daily routine differs from the classic picture of hippos resting in broad freshwater rivers. On Orango they make use of:

Researchers believe this behaviour reflects the unusual geography of the archipelago rather than any special physiological adaptation to seawater. They still depend on freshwater sources and terrestrial grazing, but they are remarkably comfortable navigating environments shaped by ocean tides.[Fundación Biodiversidad]fundacion-biodiversidad.esFundación BiodiversidadImproving the food security of the Bijago population and…The project aims to resolve conflicts between rice cro…

This distinction matters because popular travel writing sometimes exaggerates the claim into the idea that the animals “live in the sea”. The evidence instead shows a population living within an intricate coastal mosaic where marine and freshwater habitats overlap.

Sacred islands and protected wildlife

The hippos are only one part of a much broader relationship between culture and conservation in the Bijagós.

Many islands are regarded by the Bijagó people as sacred places associated with ancestors, rituals and traditional authority. Some islands remain largely uninhabited because access has long been restricted by religious custom, while others contain sacred forests, initiation sites or ritual landscapes. Estimates suggest that a large proportion of the archipelago’s islands possess some form of sacred status.[Sacred Natural Sites]sacrednaturalsites.orgAlmost three quarters of all 88 islands in the archipelago are…Read more…

These beliefs have had practical ecological consequences.

Traditional restrictions have often limited hunting, tree cutting and permanent settlement in sensitive areas. Long before international conservation programmes arrived, local customs helped preserve habitats that today are recognised as internationally important for biodiversity.

One striking example is Poilão Island. The island has long been considered sacred, and traditional rules limiting disturbance helped protect what scientists later confirmed is one of the Atlantic Ocean’s most important nesting sites for green sea turtles. Modern conservation builds on, rather than replaces, these older traditions.[ResearchGate]researchgate.netResearchGate(PDF) First census of the green turtle at Poilifilo, Bijagos…This study confirmed that Poilão is one of the most important…

In this sense, the “mystery” is not supernatural wildlife but the way spiritual geography and ecological protection reinforce one another.

Where wonder meets ecology

The Bijagós illustrate an important pattern found in several parts of Africa: places described in folklore as spiritually powerful often turn out to be biological refuges.

For sceptics, the explanation is straightforward. Sacred taboos reduced human disturbance, allowing vulnerable species to survive where they might otherwise have disappeared.

For local believers, the direction of cause and effect is often reversed. The abundance of wildlife is itself evidence that the islands remain under the protection of ancestral or spiritual forces. The continued presence of rare animals—including hippos, sea turtles, manatees and migratory birds—confirms that these landscapes deserve respect rather than exploitation.[UNESCO]unesco.orgUNESCO strengthens its support to Guinea-Bissau for the…20 Apr 2023 — They are a sanctuary for hundreds of animal species, inclu…

Neither perspective removes the fascination. Instead, they describe the same landscape through different languages: ecology on one hand and sacred tradition on the other.

Why the Bijagós matter in Guinea-Bissau’s strange history

Within Guinea-Bissau’s wider catalogue of unusual traditions, the Bijagós stand out because the remarkable claims are anchored in observable reality.

Visitors genuinely can encounter hippos using tidal channels close to the Atlantic coast. Scientists genuinely recognise the population as behaviourally unusual and conservation priorities reflect its rarity. Sacred islands genuinely exist within Bijagó culture, and archaeological, anthropological and ecological studies all show that traditional beliefs have influenced how land and wildlife have been protected.[fundacion-biodiversidad.es]fundacion-biodiversidad.esFundación BiodiversidadImproving the food security of the Bijago population and…The project aims to resolve conflicts between rice cro…

That combination makes the archipelago especially attractive to Fortean readers. It is not a story of hidden monsters or impossible beasts, but of a landscape where astonishing wildlife, ancient ritual traditions and modern conservation overlap so closely that folklore and field biology seem to illuminate one another rather than compete.

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Endnotes

1. Source: whc.unesco.org
Link:https://whc.unesco.org/en/list/1431/

2. Source: unesco.org
Link:https://www.unesco.org/en/mab/bolama-bijagos

3. Source: researchgate.net
Link:https://www.researchgate.net/publication/227943800_First_census_of_the_green_turtle_at_Poilifilo_Bijagos_Archipelago_Guinea-Bissau_the_most_important_nesting_colony_on_the_Atlantic_coast_of_Africa

4. Source: unesco.org
Link:https://www.unesco.org/en/articles/unesco-strengthens-its-support-guinea-bissau-protection-bijagos-islands

5. Source: unesco.org
Title: The Organization
Link:https://www.unesco.org/en

6. Source: researchgate.net
Link:https://www.researchgate.net/publication/234554876_Distribution_and_current_status_of_the_West_African_manatee_Trichechus_senegalensis_in_Guinea-Bissau

7. Source: researchgate.net
Link:https://www.researchgate.net/publication/271842073_The_Bijagos_Islands_culture_resistance_and_conservation

8. Source: fundacion-biodiversidad.es
Link:https://fundacion-biodiversidad.es/en/proyectos_ficha/improving-the-food-security-of-the-bijago-population-and-the-conservation-of-the-hippopotamus-in-the-orango-national-park-guinea-bissau/

9. Source: sacrednaturalsites.org
Link:https://sacrednaturalsites.org/items/increasing-recognition-for-sacred-natural-sites-in-coastal-regions-in-guinea-bissau/

10. Source: bijagos.com
Link:https://bijagos.com/

11. Source: ceibabissau.com
Title: saltwater hippos
Link:https://ceibabissau.com/saltwater-hippos/

12. Source: prcmarine.org
Link:https://www.prcmarine.org/bijagos/article/10759

Additional References

13. Source: responsibletravel.com
Link:https://www.responsibletravel.com/holidays/guinea-bissau/travel-guide/the-bijagos-archipelago

14. Source: got2globe.com
Link:https://www.got2globe.com/en/editorial/orango-marine-hippos-bijagos/

15. Source: mava-foundation.org
Link:https://mava-foundation.org/library/sacred-islands-how-community-and-culture-are-driving-sustainability-in-the-bijagos-archipelago-and-beyond/

16. Source: iucn.org
Title: protecting chimps hippos and turtles iucn recommends five new world heritage
Link:https://iucn.org/press-release/202505/protecting-chimps-hippos-and-turtles-iucn-recommends-five-new-world-heritage

Published: May 2025

17. Source: consulmartravel.com
Title: To reach it, it is necessary to travel first to Bissau and then take a speedboat
Link:https://www.consulmartravel.com/en/orango-and-its-saltwater-hippopotamus-a-unique-destination-in-the-world/

18. Source: seaturtlestatus.org
Title: conservation progress in the bijags archipelago guinea bissau
Link:https://www.seaturtlestatus.org/articles/2016/conservation-progress-in-the-bijags-archipelago-guinea-bissau

19. Source: eu-space.europa.eu
Title: tidal landscapes bijagos archipelago guinea bissau
Link:https://eu-space.europa.eu/components/earth-observation-copernicus/image-of-the-day/tidal-landscapes-bijagos-archipelago-guinea-bissau

20. Source: orangohotel.com
Title: hippos on the island of orango guinea bissau
Link:https://www.orangohotel.com/en/hippos-on-the-island-of-orango-guinea-bissau/

21. Source: responsiblevacation.com
Title: Bijagos Archipelago in Guinea-Bissau
Link:https://www.responsiblevacation.com/vacations/guinea-bissau/travel-guide/the-bijagos-archipelago

22. Source: iucnsos.org
Title: new national parks for guinea bissau
Link:https://iucnsos.org/new-national-parks-for-guinea-bissau/