High Park Underground: What Lies Below the Park
Discover the hidden world beneath Toronto’s High Park, where historic sewer tunnels and infrastructure reveal fascinating stories of early city planning and engineering.
Entombed beneath the landscape of High Park’s northeast corner lies a complex network of early 20th‑century sewer infrastructure. The most significant of these hidden structures is the High Park Trunk Sewer, installed along the park’s northern boundary in 1914 as part of a major citywide effort to fill ravines and pave the way for new residential development in Toronto. As part of this process, large portions of both Spring Creek and Wendigo Creek ravines were buried to create a level grade along Bloor Street, and make the surrounding land far easier to develop.
High Park Trunk Sewer (Built in 1914)
The trunk sewer begins just east of Jane Street and runs beneath Bloor Street, travelling eastward toward the vicinity of High Park Avenue. There, it turns southeast into the park, passing close to the now‑disused Parkside Standby Tanks. The sewer’s structure changes along its route: it starts as a low rectangular passageway, descends a series of steps east of Runnymede Road, and expands into a brick‑and‑concrete arch roughly two metres tall near Clendenan Avenue. Along its course, it connects with a sub‑trunk sewer from the north and receives a side connection serving the apartment towers northwest of Bloor and Keele. This connection is often noted for its strong chlorine and ammonia odours.
Constructed in 1914, the High Park Trunk Sewer began as a modest brick‑arch passageway designed to carry wastewater beneath the newly filled ravines along Bloor Street. After installation, the sewer was buried under extensive landfill.
South of Bloor Street, the line connects to the now‑disused Parkside Drive Standby Tanks — large, 2.7‑metre‑wide brick conduits originally built to provide overflow capacity during periods of heavy wastewater flow. Beneath these massive chambers runs a smaller sewer pipe that once served as part of the area’s relief network. From this point, the system continues straight down Parkside Drive toward Lake Ontario, forming a critical link in Toronto’s early wastewater management system.
Though superseded by more modern infrastructure today, these buried structures serve as relics to long-lost ravines and creeks, and early engineering efforts that enabled the Toronto’s rapid growth in the early‑20th‑century.
Additional concrete storm sewers were constructed at the same time. These channel stormwater into what remains of Spring Creek and Wendigo Creek, discharging through outfalls at the sediment ponds within High Park, including Ridout Pond and Howard Pond. In the park’s northeast corner, a small pipe diverts flow from the trunk sewer into the High Level Interceptor, part of a broader system that manages wastewater across the city.
Diversions, Upgrades, and Modern Infrastructure
By the 1970s, Toronto added further infrastructure to ease the strain on the High Level Interceptor. A tall side‑flow weir and adjacent concrete shaft, housed within a diversion chamber, were built to redirect excess flows during heavy rains. When these overflows occur today, wastewater drops roughly 15 feet into a modern conduit that carries it to the Parkside Drive Relief Sewer.
Originally, the Parkside sewer discharged directly into Lake Ontario. Since the early 2000s, however, it has been integrated into the Western Beaches Storage Tunnel, ensuring that combined sewer overflows are captured and treated rather than entering the lake.
Special thanks to Karyn Klaire Koski for her valuable contributions to the content on this webpage.
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