Veiga de S. Simão is a wetland located on the left bank of the Lima River estuary, occupying about 700 hectares along the parishes of Darque, Mazarefes, Subportela and Vila Franca.
In ecological terms, this is one of the most important wetlands in the municipality, with complex systems of reeds, salt marshes and reeds that, together with the Lagoons of Vila Franca, require specific and pertinent conservation measures and attention.
These places serve as a place to feed and shelter several species of shorebirds and waterfowl, namely wintering and migrating species.
In drier areas, out of the reach of marine waters, agricultural spaces and forests are spread out over 200 hectares.
In this area, there has been an important human interaction over time, which has allowed the existence of an agricultural space drained and traversed by several channels, transforming salty land into arable areas of high fertility. In this way, the drainage system limited the progression of marine waters inland, and the land closer to the river still works today as protection for the more inland land.
This ecosystem has undergone changes that constitute threats to biodiversity and habitat conservation, namely due to the proliferation of invasive species and human pressure.

In this place, inserted in the Lima River SCZ, the habitats contained in the Habitats Directive occur:

• 1140 - Mudflats and sands uncovered at low tide
• 1130 - Estuaries
• 1330 - Atlantic salty meadows (Galuco-Puccianellietalia maritimae)
• 1310 - Pioneer vegetation of Salicornia and other annual species in muddy and sandy areas
• 1320 - Meadows of Spartina (Spartinion maritimae)
• 1420 - Mediterranean and thermo-Atlantic halophytes (Sarcocornetea fruticosi)
• 91E0* - Alluvial florets of Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae) - priority habitat.