From Ayamonte you can choose some different types of Guadiana river cruises. The company that is managed by the Guadiana River Transport is called SL and they all start from the dock and then go to the fishing port of Ayamonte, where you can purchase the ticket (although in summer keep in mind that seating is limited, so reserve ahead). Last year I made the cruise to Sanlucar de Guadiana River. It's a pretty full day excursion, it leaves about 10 am and returns about 17h. The boat has a portion that goes upstream, and you get to view the landscape and the lush vegetation, as well as the tropical nature of the place, and the tons of different birds (herons, storks, black vultures ...). The journey to get to Sanlucar de Guadiana takes about 2 ½ hours, and meanwhile, offer drinks and snacks (Huelva prawns and pork), accompanied by music. Once in Sanlucar have free time to visit this small town that has preserved its typical traditional style. Then they take you to a small restaurant where they serve food (included), and we start the journey back to Ayamonte.
From here you can see the mouth of the Rio Guadiana. In the background, you can see the magnificent suspension bridge linking Spain with Portugal on the border of Ayamonte. To access the end of the Huelva coast, you have to wait until the tide goes out. It's worth taking a stroll down the coast to get to this place.