Hi!
Last Saturday, while spending some time in the city of San Pedro, Buenos Aires, I took my daughter to see the Paraná River. It has grown a lot since the last time we had been there (last year there was a big drought and we are just now recovering). What you see in the photo is actually just one of the side branches of the river, which in this area has several islands. The main branch is much wider. The river is not particularly polluted. The brown color you see in the photo is its natural color, as the bed is made of mud. In some areas, in fact, the river forms beaches and it is possible to bathe. Greetings!