As more than 300 fish are discovered perished in a Pennsylvania, USA waterway during the week of July 22, 2011, chlorine is also detected coming from a public swimming pool, with environmental officials saying that the toxic chemical along with a heat wave and another pollutant spill likely caused the fish's deaths.

http://articles.philly.com/2011-07-22/news/29802177_1_dead-fish-chlorinat
http://www.newsworks.org/index.php/local/item/23496-fish-kill-in-cobbs-creek

With the dead zone in the Gulf of Mexico off the US coast already measuring 3,300 square miles (5,300 square kilometers) as of June 2011, US researchers at the end of July state that the oxygen-deprived area, fed by warming waters and nitrates from Mississippi River runoff, is expected to be the largest ever this year.

http://www.sott.net/articles/show/232420-U-S-Mississippi-Runoff-Expands-Gulf-Dead-Zone
http://www.sott.net/articles/show/232418-U-S-Alarming-dead-zone-grows-in-the-Chesapeake