In collins dictionary I have seen the following sentence, which gets me confused. https://www.collinsdictionary.com/dictionary/english/flood
Over 25 people drowned when a schoolbus tried to cross a river and flood waters swept through.
We know that the word is "uncountable", so there won't be a plural form of it with -s suffix. We can't say waters, can we?
Then if the same rule applies, it must be used as "flood water" not "flood waters". But then why does the dictionary uses it "flood waters".