【正确答案】Dear Sir or Madam,
I'm writing the letter to express my deepest concern about the water pollution in the nearby river.
It must be pointed out that the current situation is going from bad to worse. Therefore, it's imperative for the local authorities to adopt some drastic measures. To begin with, we should enhance the public's awareness of the gravity of this problem, which is of vital importance to the solution. Secondly, a series of rules and regulations should be laid down as soon as possible and those who violate it shall be fined heavily. Finally, the chemical plant by the river must be prohibited from discharging waste water into the river before it is purified.
Thank you for paying due attention to this letter. I am expecting to see new changes in the river.