Port de l'Estany, or Port de l'Estany Gras, is a small natural port that forms at the mouth of the Estany ravine, between Punta de l'Estany, to the east, and the beach of l'Estany Lake, to the west. It forms a typical coastal lagoon but, in this case, it is not separated from the sea by a strip of beach but the final section is open to the sea and functions as a small natural port. Also included in the space is an area, crossing the road, with stagnant water. In this old natural port, fishermen moored their boats there until 1920, when the Port of Ametlla de Mar was built.

The bottom of the lagoon is mostly covered by the charophyce Chara hispida. The vegetation on the surface varies according to its proximity to the sea: reedbeds on the edge of the lagoon and meadows and halophilic rushes of Scirpus holoschoenus, Juncus acutus, etc., closer to the sea. In the area of stagnant water there is an extensive area of reeds and reed beds.

In terms of fauna, it is a sapce that is of great interest for the conservation of fish species from brackish environments but is little used by birds from wetlands.

The area is part of the PEIN "Cap de Santes Creus" and is also included in the Natura 2000 Network ES5140001 Southern Tarragona Coast.