We still dump untreated sewage into the sea all round the UK. OK, it's not as prevalent as it was (most of South West Water's sewage was untreated until the mid-1990s, hence "Surfers Against Sewage"), but it's still happening.
The trouble with humans as opposed to other species is that we've worked out how to make tools, fire, chemicals and split the atom which infinitely multiply our destructive powers. Our nearest animal cousins have barely started on the first of those. I remember a story where ants somehow acquired the gift of fire - it's a scary prospect, because even the smallest creature can burn the world.