Question: The Kiev water supply was switched to the Desna River how many months after the Chernobyl disaster?
About the article "Chernobyl disaster", section "Rivers, lakes and reservoirs".

Candidate passages:
Residual radioactivity in the environment.
Rivers, lakes and reservoirs.
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, though officially it was stated that all contaminants had settled to the bottom "in an insoluble phase" and would not dissolve for 800–1,000 years.
Guidelines for levels of radioiodine in drinking water were temporarily raised to 3,700 Bq/L, allowing most water to be reported as safe, and 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 abruptly switched from the Dnieper to the Desna River.
Meanwhile, massive silt traps were constructed, along with an enormous 30m-deep underground barrier to prevent groundwater from the destroyed reactor entering the Pripyat River.
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 1,000 Bq/kg in the European Union.
In the Kiev Reservoir in Ukraine, concentrations in fish were several thousand Bq/kg during the 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.
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Pripyat (; ) is an abandoned city in northern Ukraine, near the border with Belarus.
Named for the nearby Pripyat River, Pripyat was founded on 4 February 1970, the ninth nuclear city in the Soviet Union, for the Chernobyl Nuclear Power Plant.
It was officially proclaimed a city in 1979, and had grown to a population of 49,360 before being evacuated a few days after the 26 April 1986 Chernobyl disaster.
Though Pripyat is located within the administrative district of Ivankiv Raion, the abandoned city now has a special status within the larger Kiev Oblast (province), being administered directly from Kiev.
Pripyat is also supervised by Ukraine's Ministry of Emergencies, which manages activities for the entire Chernobyl Exclusion Zone. 
Desna () is an urban-type settlement in the Chernihiv Oblast in northern Ukraine.
The town's population was 7,180 as of the 2001 Ukrainian Census and 7,562 in 2011.
It is named after the Desna River which flows through the town. 
Slavutych () is a city in northern Ukraine, purposely-built for the evacuated personnel of the Chernobyl Nuclear Power Plant after the 1986 disaster that occurred in the city of Chernobyl.
Geographically located within the Ripky Raion, Chernihiv Oblast, Slavutych is administratively subordinated to the Kiev Oblast as a "city of regional significance".
As of 2007, the city population was 24,549.