There are a number of dams along the course of the river Douro and this one, close to Regua da Peso has a massive lock for the passing cruise boats. It also has lots and lots of nesting swifts in the small pipes in the sheer concrete walls.
We were so high that we were looking down onto the swifts. It was a challenge not only to get a fast eough shutter speed and to track the birds but mainly to endure the 40 degree blazing sun!
