The Lima valley in the municipality of Viana do Castelo has wide and flat margins, in a agricultural landscape, with the occasional occurrence of riparian and forests galleries. In the lower zone of the estuary, the river extends and appears in the riverbed, mainly in the middle estuary, due to the deposition of sediments by contact with the saline wedge of marine origin. Despite human occupation throughout its extension, the area further up the estuary has a significant degree of conservation.
Due to human occupation, the Lima River estuary has been severely modified by anthropic action, namely with regard to the artificial consolidation of margins.
So, the area corresponding to the low estuary, formerly occupied by sands of marine origin and fine sludge, is currently occupied by the commercial port facilities. Despite these changes, there are spaces in the estuary where the typical vegetation of medium and high estuaries is well represented, with a set of estuarine wetlands very interesting at an ecological level, such as Veiga de S. Simão, the lagoons of Vila Franca, the marshland da Meadela and the current Urban Ecological Park of Viana do Castelo (PEUVC) which, although not within the limits of the Special Conservation Zone (SCZ), represents an important biotope in ecological terms.

The Lima River Special Conservation Zone extends over 5382 hectares, of which 1891 hectares (about 35%) are within the boundary of the municipality of Viana do Castelo.
In this SCZ, there occurs 13 biotopes from Annex I of the Habitats Directive, 2 of which are considered priority. The priority habitat formed by groves of white oak (Quercus robur) has little expression, having been almost entirely replaced by eucalyptus forest plantations (Eucalyptus globulus) and maritime pine (Pinus pinaster).