more on the lagoon

Not trying to be argumentative, Katherine, but if the counterclockwise current idea is correct, any pollution from Las Salinas should be entering the Bay after Playa Principal, not before it. The worst beaches in the Bay, then, would be those little ones past the entrance/exit of Las Salinas. Fortunately, (as it turns out), there's no longer any easy public access to those beaches, if at all.

The currents aren't as simple in the bay as you describe them. Waves and tides and the contours of the coast all have their effects. The worst beach in the bay is indeed Playa El Almacén, thanks to the jetty at Puerto Mío, which may be why Puerto Mío denies that beach even exists. Several years ago the government used to test the water there. No testing is done at Contramar either. Those are the "little ones" you refer to.