This natural area is an interesting remaining of a biologically rich vast wetland that was partially dried and filled during the 20th century. Twice a day Cantabrian sea high tides flood this marsh, producing a high valuable ecosystem of specific Flora and Fauna species, including long-legged and wading birds as eventual visitors. Each year at the end of the summer, herons, cormorants, sandpipers and other migratory birds come from the north and stop at this natural environment to have an indefinite stop on their trip to the south. Yet, shy moorhens, ducks and introduced domestic geese use the reedbeds on this park for nesting all year. The promenade along the wetland has discreet wooden spots for birders. 

At the western end of El Malecón promenade El Pilar stone bridge, built during the 18th century, points out the first solid ground surrounding the sandy beach and the old marsh. Apart, a play area for children, with sledges and swings, is displayed at the eastern end of this park.