Urdaibai estuary

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The Urdaibai estuary

The Urdaibai estuary is a natural region and a Biosphere Reserve of Biscay, Basque Country, Spain. It is also referred as Mundaka or Gernika estuary.

Urdaibai is located on the Bay of Biscay coast, in the north of the Iberian Peninsula. Urdaibai covers an area of 220 km2 (85 sq mi) with some 45,000 inhabitants, most of them concentrated in the towns of Bermeo and Gernika. The territory is characterized by a hydrographic basin of small streams that merge in a great salt marsh surrounded by high sheer cliffs. The surrounding countryside is occupied by meadowland, oak groves, leafy woods and specially by plantations of fast-growing conifers (Pinus radiata). The coastal landscape is covered with Cantabrian woods of Holm Oak and Strawberry Trees.

In Urdaibai have been described 615 species of vascular plants and 318 species of vertebrates, 245 of which are birds.

The area contains remnants of the Prehistoric, Roman and the Middle Ages. Particularly notable is the Santimamiñe cave, which has yielded archeological artifacts from the Mousterian (Middle Paleolithic Age) to the Iron Age.

The economy is based on metallurgy, fishing, farming and forestry. An important tourist sector is based on the quality of the local beaches. Mundaka is especially appealing for surfers around the world.


The Oca river arises in the Oiz mountain and finishes in the Cantabric sea. The coast is rugged and with high cliffs and some islands, of which the most important is Izaro Island.

Izaro island

The development of forests reserves have allowed a degree of environmental conservation, which gives this area the most diverse landscape of the Basque Country.

Climate and temperature[edit]

The area of Urdaibai has an Atlantic climate, wet and warm and regulated by the sea (with temperature between 9-19 degrees C.) The annual rainfall is heavy; the rainiest months are November and December, although it is distributed during all the year. Precipitation is generally rain. Because of the influence of the sea, the temperature is moderate during the year (the average temperature is 13/14 degrees).


Oka's marshes

The landscape is formed with mountains, sea and sands, which are produced by the sediments of the estuary, where marshes are flooded by the tides. The rivers Laga and Artigas go directly to the sea. The first ends in Laga´s beach, and the second one creates a small valley between the Sollube mountain and Bermeo.


The estuary is the heart of the Biosphere's Reserve, which is a habitat for a wide variety of migrating and resident birds. The estuary with Santoña´s natural park is the most important wetland in the Iberian Peninsula.

The interior is defined by the mountains, and on their slopes are forest plantations of Monterey Pine used to make wood. There also are a few forests with local trees, such as Oak; and near the coast are plantations of Eucalyptus. On the central area, the land becomes flat and it is used in agriculture. This landscape is supported by livestock and agricultural development. The estuary extends from Guernica to Busturia, and a 5 km canal has been made in order not to dry up.


The slopes of the mountains are covered by forests of holm oaks down to the sea's edge. The limestone nature of the bedrock has led to a kast system, where numerous caves and galleries may be found.


Laida's beach

On the north, at the mouth of the estuary, the sands of Sukarrieta and Laida line the shore of the Oka River.

On the west are the sands of Santa Katalina, Murgoa and Lamera. The Murgoa has a slope of a hundred meters, forming places like Trankilpunta and Kargaderua. After Bermeo, are found the cliffs of Talape and Tonpoi. In the flysch that is made on the foot of cliff, there can be found the " Arribolak", large stones which have been released from the wall and later rounded by the sea. On the east the sea stops being rough.

Flora and Fauna[edit]


The flora that is developed in Urdabai, is clearly an atlantic base. There are a lot of meadows, oak groves, lush forests and especially plenty of Monterey pines. The coastal area is covered by cantabrian forests. The vegetable world that can be found overthere, is formed by 615 species of plants. The human activity has modified substantially the espace, but the agricultural works have allowed the recuperation of original vegetation. The vegetation has, mainly in the marsh, a grade of singularity because of the specialization and also and its particular appearance. However, at the same time it has a high grade of diversity originated by the salinity. The area of Urdaibai is composed by different environments, each of which has its own vegetation and animals that create their own ecosystem.

  • The coast
  • Mountain of the left side
  • Middle tract of the Oka and its tributaries
  • Closed valleys from the Oka
  • Karstic area and the environment of the right side
  • Guernica and Mundaka´s valley


The big variety of ecosystems that can be found in the Urdaibai make possible the faunistic wealth, with 318 species of vertebrates, apart from the amount of different birds.

  • Fishes in the head of the river there are trout, eels and loachs mainly, while in the middle we found barbels.
  • Amphibians although they are too much in danger, lost of salamanders, toads and different kind of frogs are common in there.
  • Aves the birds are the most important part of fauna in Urdaibai. Most of them emigrate from Europe to Africa and in the other way. Some of them are, black storks, herons, eagles.[1]
  • Mammals in this group we can difference little and big animals. The fist ones are, for example: moles, shrews, dormice...


There are four distinct areas of interest in the reserve:

  • The estuary.
  • The shores.
  • Holm Oak areas.
  • Archeologic areas.

Geographically three distinct areas can be distinguished: The mountains, the marshes and the coast with its cliffs and beaches.



Coordinates: 43°19′56″N 2°40′19″W / 43.33222°N 2.67194°W / 43.33222; -2.67194