I’ve heard that there are several buried rivers in Toronto

Dear Urban Decoder: I’ve heard that there are several buried rivers in Toronto. Where are they located and why were they covered over?—Alex Berry, Woodbine Heights

Toronto’s groundwater is now mostly hidden, but dozens of creeks and streams did indeed once burble through the downtown core and beyond. Big ones included Taddle Creek, trickling beneath Philosopher’s Walk at U of T, and Garrison Creek, which wended its way through Trinity Bellwoods before heading toward Fort York. The financial district was laced with watercourses—Station Creek ran past Union, while Cathedral Creek flowed past St. James’ Cathedral on King. These and other waterways were forced underground in the late 19th and early 20th centuries, after our garbage had turned them into festering health hazards. The big ones were converted to sewer lines, as in the case of both Taddle and Garrison. (In the late 1880s, the latter was entombed in an approximately two-metre-diameter brick pipe, which is still used by the city to carry sewage.) The creeks in the financial district were filled by countless tonnes of earth and concrete.

Toronto’s oldest lost river is the once mighty Laurentian, which connected Lake Ontario with Georgian Bay. It was buried about a million years ago by glacial debris but trickles on through the soft sand beneath High Park—at a stately pace of one centimetre per year.