How do you say 時は真夏、ずっと前なら、どこの川でも子供達が遊んでいたのだが、今ではそれも水質汚濁のせいで稀なこととなった。 in English?

It is the middle of summer, when, many years ago, children could be seen playing in every river, which is now quite rare, however, owing to water contamination.