Water outflows from nuclear plants expel relatively warm water which can have adverse local impacts in bays and gulfs, as can heavy metal and salt pollutants. The US Environmental Protection Agency states: "Nuclear power plants use large quantities of water for steam production and for cooling. Some nuclear power plants remove large quantities of water from a lake or river, which could affect fish and other aquatic life. Heavy metals and salts build up in the water used in all power plant systems, including nuclear ones. These water pollutants, as well as the higher temperature of the water discharged from the power plant, can negatively affect water quality and aquatic life. Nuclear power plants sometimes discharge small amounts of tritium and other radioactive elements as allowed by their individual wastewater permits."
A report by the by the US Nuclear Information and Resource Service (NIRS), US Humane Society and other groups, 'Licensed to Kill: How the Nuclear Power Industry Destroys Endangered Marine Wildlife and Ocean Habitat to Save Money', details the nuclear industry's destruction of delicate marine ecosystems and large numbers of animals, including endangered species. Most of the damage is done by water inflow pipes, while there are further adverse impacts from the expulsion of warm water. Another problem is 'cold stunning' – fish acclimatise to warm water but die when the reactor is taken off-line and warm water is no longer expelled. For example, in New Jersey, local fishers estimated that 4,000 fish died from cold stunning when a reactor was shut down. (See the report and 6-minute video at www.nirs.org/reactorwatch/licensedtokill and the video is also posted at www.youtube.com/watch?v=VVsw3rmCnnU)
Case Study: Close to one million fish and 62 million fish eggs and larvae died each year when sucked into the water intake channel in Lake Ontario, which the Pickering nuclear plant uses to cool steam condensers. Fish are killed when trapped on intake screens or suffer cold water shock after leaving warmer water that is discharged into the lake. The Canadian Nuclear Safety Commission told Ontario Power Generation to reduce fish mortality by 80% and asked for annual public reports on fish mortality.
Case Study: The Oyster Creek nuclear plant in New Jersey, US, has killed 80 million pounds (36,300 tonnes) of aquatic organisms in the Barnegat Bay over the past 40 years, according to the US Fish and Wildlife Service.
 US Environmental Protection Agency, 'Nuclear Energy', www.epa.gov/cleanenergy/energy-and-you/affect/nuclear.html
 Carola Vyhnak, 6 July 2010, 'Pickering nuclear plant ordered to quit killing fish', 'Millions of adults, eggs and larvae perish when sucked into intakes or shocked by cold water', www.thestar.com/news/gta/article/832748--pickering-nuclear-plant-ordered...
 Todd Bates, 22 March 2012, 'Oyster Creek nuclear plant kills 1,000 tons of sea life a year, agency says', http://blogs.app.com/enviroguy/2010/03/22/oyster-creek-nuclear-plant-kil...