There is a small boat museum at Guerreiros do Rio where there is a fine display of model boats as well as a video presentation. The museum indicates that the river was once a busy place not only for fishermen but also for Customs on the look out for smugglers. The old Customs House is in Alcoutim near the river crossing, it now houses the tax office.
As well as the museum there is a nice little cafe alongside the river where you can get a drink and a snack and where there's a wifi hotspot.
There has been a fortification at Alcoutim for a couple of thousand years with the Romans having an impact in developing the area as a military base. in the former gunpowder of the castle there is a display (Timeless Games) of stone games boards (a bit like 9 Men Morris) from this period.
We have been to Alcoutim a couple of times and of course from here you can go on to Mertola and Castro Verde for starters but that's for another entry another time.