page_title: Chernobyl disaster
section_title: Water bodies
hierarchical_section_title: Chernobyl disaster / Environmental impact / Water bodies
caption_attribution_description: English: This true-colour picture shows the nuclear reactor. The large body of water in the left half of the image is the north-western end of a 12-kilometre long cooling pond, and water channels run through the network of reactor-related buildings west of the pond. Reactor number four appears on the west end of a long building north-west of the right-angled L-shaped water channel. Mixing with the network of abandoned buildings, water channels, and roads, areas of green appear—a testament to the vegetation that was growing around the site some 20 years after the accident.
context_page_description: The Chernobyl disaster was caused by a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR. It is considered the worst nuclear disaster in history and was caused by one of only two nuclear energy accidents rated at seven—the maximum severity—on the International Nuclear Event Scale, the other being the 2011 Fukushima Daiichi nuclear disaster in Japan.
  The accident started during a safety test on an RBMK-type nuclear reactor, which was commonly used throughout the Soviet Union. The test was a simulation of an electrical power outage to aid the development of a safety procedure for maintaining reactor cooling water circulation until the back-up electrical generators could provide power. This gap was about one minute and had been identified as a potential safety problem that could cause the nuclear reactor core to overheat. It was hoped to prove that the residual rotational energy in a turbine generator could provide enough power to cover the gap. Three such tests had been conducted since 1982, but they had failed to provide a solution.
context_section_description: The Chernobyl nuclear power plant is located next to the Pripyat River, which feeds into the Dnieper reservoir system, one of the largest surface water systems in Europe, which at the time supplied water to Kiev's 2.4 million residents, and was still in spring flood when the accident occurred. The radioactive contamination of aquatic systems therefore became a major problem in the immediate aftermath of the accident.
  In the most affected areas of Ukraine, levels of radioactivity (particularly from radionuclides ¹³¹I, ¹³⁷Cs and ⁹⁰Sr) in drinking water caused concern during the weeks and months after the accident, Guidelines for levels of radioiodine in drinking water were temporarily raised to 3,700 Bq/L, allowing most water to be reported as safe, 
   Officially it was stated that all contaminants had settled to the bottom "in an insoluble phase" and would not dissolve for 800–1000 years.
  A year after the accident it was announced that even the water of the Chernobyl plant's cooling pond was within acceptable norms. Despite this, two months after the disaster the Kiev water supply was switched from the Dnieper to the Desna River. Meanwhile, massive silt traps were constructed, along with an enormous 30-metre (98 ft) deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River.
  Groundwater was not badly affected by the Chernobyl accident since radionuclides with short half-lives decayed away long before they could affect groundwater supplies, and longer-lived radionuclides such as radiocaesium and radiostrontium were adsorbed to surface soils before they could transfer to groundwater. However, significant transfers of radionuclides to groundwater have occurred from waste disposal sites in the 30 km (19 mi) exclusion zone around Chernobyl. Although there is a potential for transfer of radionuclides from these disposal sites off-site (i.e. out of the 30 km (19 mi) exclusion zone), the IAEA Chernobyl Report argues that this is not significant in comparison to current levels of washout of surface-deposited radioactivity.
  Bio-accumulation of radioactivity in fish resulted in concentrations (both in western Europe and in the former Soviet Union) that in many cases were significantly above guideline maximum levels for consumption. Guideline maximum levels for radiocaesium in fish vary from country to country but are approximately 1000 Bq/kg in the European Union. In the Kiev Reservoir in Ukraine, concentrations in fish were in the range of 3000 Bq/kg during the first few years after the accident.
  In small "closed" lakes in Belarus and the Bryansk region of Russia, concentrations in a number of fish species varied from 100 to 60,000 Bq/kg during the period 1990–92. The contamination of fish caused short-term concern in parts of the UK and Germany and in the long term (years rather than months) in the affected areas of Ukraine, Belarus, and Russia as well as in parts of Scandinavia.
  Chernobyl's radiocesium deposits were used to calibrate sedimentation samples from Lake Qattinah, Arabic: بحيرة قطينة in Syria. The ¹³⁷
  ₅₅Cs
   provides a sharp, maximal, data point in radioactivity of the core sample at the 1986 depth, and acts as a date check on the depth of the ²¹⁰
  ₈₂Pb
   in the core sample.
caption: Reactor and surrounding area in April 2009
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