This trail has been planned with the observation of water birds in mind. It passes through the thickets on the bank of the River Gállego, at the section from Biescas to Oliván, an area that has been declared an SCI (Site of Community Importance) in the Natura 2000 network.
On the N-260 from Sabiñanigo to Biescas, take the turn-off for Oliván, crossing the bridge over the River Gállego. Leave the car and walk to the left-hand side in order to get to the river. The kingfisher, which has spectacular electric blue plumage, lives on the banks of the river.
Around the river you can also see white wagtails, a small bird with a long tail that is constantly moving, up and down. It is unmistakeable with its black and white coloured feathers.
One of the smallest birds in Europe hides among the bushes and branches along the banks of the river: the wren. Its brown plumage makes an excellent camouflage so it is difficult to see.
When you have finished your walk along the riverbank drive south east to the riverbank woods. This has become one of the most important wintering areas for the grey heron. There are around 30 breeding pairs here and approximately 150 birds spend the winter.
In winter the great cormorant uses this wood to roost. This is a sea bird that spends the winter on rivers and inland reservoirs. They have dark plumage, and in many languages are called the sea raven.
The riverbank woods with their popular trees, willows, crack willows and elms are home to the European green woodpecker, a green and yellow woodpecker. Its call is very distinctive as it sounds like neighing.
During the summer time you can see black kites in the area around the fish factory. These are a dark-coloured, medium-sized bird of prey and they fly here from Africa in late spring.