Most rivers have rich, dense vegetation on their banks. This vegetation is normally highly diverse and the whims of the water create corners and environments of very different natures: treed areas, bushes, brambles, stones, reeds, etc.
Among the most frequent tree species figure the alder (mainly beside rivers in the green Navarre), willow, poplar, crack willow, black poplar, hazel, etc.Birds:
The speed and small dimensions of mountain rivers in the north means that they only attract a few species of bird. The rivers in the centre and the south, which run over flatter terrain, are slower and contain more water, thereby appealing to many more. The green vegetation surrounding the latter also makes them a true oasis within a far dryer environment, alluring many species which would otherwise ignore their existence.
It is normal to see the Dipper and Grey Wagtail in the waterways of the north; the Sisken should be highlighted in alder copses in the winter.
In the other rivers, the range of birds is much wider: the Mallard, Great Cormorant, Grey Heron, Purple Heron, Little Egret, Black Kite, Hobby, Moorhen, Little-ringed Plover, Common Sandpiper, Scops Owl, Common Kingfisher, Wryneck, Great Spotted Woodpecker, Lesser Spotted Woodpecker, European Bee-eater, Hoopoe, Sand Martin, White Wagtail, Wren, Robin, Blackbird, Song Thrush, Rufous Nightingale, Cetti?s Warbler, Melodious Warbler, Olivaceous Warbler, Garden Warbler, Blackcap, Iberian Chiffchaff, Golden Oriole, Great Tit, Blue Tit, Short-toed Treecreeper, Penduline Tit, Magpie, Carrion Crow, Tree Sparrow, Common Chaffinch, European Serin, Greenfinch, Goldfinch, Cirl Bunting and Reed Bunting.