Q: This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
Today both the Papireto river and the Kemonia are covered up by buildings. However, the shape of the former watercourses can still be recognised today, because the streets that were built on them follow their shapes. Today the only waterway not drained yet is the Oreto river that divides the downtown of the city from the western uptown and the industrial districts. In the basins there were, though, many seasonal torrents that helped formed swampy plains, reclaimed during history; a good example of which can be found in the borough of Mondello.
A:
How can former rivers be recognised presently?