The persistent haze over many of our cities is a reminder of the polluted air that we breathe, over 80% of the world's urban population is breathing air that fails to meet World Health Organisation guidelines.
2019年12月六級(jí)真題（第二套）閱讀 Section A
Now that Chicago's waste water was draining efficiently into the Chicago river, the city's next step was to clean the polluted river.
2015年高考英語湖南卷 閱讀理解 閱讀B 原文
The river was so polluted that it actually caught fire and burned.
2014年高考英語全國卷1 語法填空 原文
While there are amazing stories of instant transformation, for most of us the changes are gradual and require a lot of effort and work, like cleaning up a polluted river.