Masked snipers are guarding Czech reservoirs after a blackmailer threatened to poison the water supplies for an entire region.
Police in the north Bohemian Liberec region received an unsigned letter from a blackmailer who demanded £230,000 sterling or else he would poison water supplies.
Special police squads are now watching over the region's two water dams.
The recent case is the fifth blackmail attempt in the Czech Republic in the last three months.
In March an unknown man threatened to plant bombs in the northern Moravia area if he is was not paid £230,000. Although police dropped the money where they were asked to, the blackmailer never collected.
Last month police arrested a man (30) for threatening to poison hospitals food supplies with cyanide and in May a 19-year-old man said he would blow up parts of Prague and Brno.
Police are also looking for another anonymous blackmailer who demanded £460,000, saying he would plant bombs in the capital if he did not get his cash.
PA