The answers are pretty much the same: Most of it, either directly or indirectly (via rain sewers, for example, or runoff from rubbish dumps) winds up in the river.
所有的答案都一樣﹘ ﹘他們絕大部分直接、間接（比如雨水排水溝，圾垃場滲漏水）流進了河裡。