The Thornbury Fishway: Then and Now

Image of Thornbury Fishway from side view.

It’s an iconic feature in Thornbury, one everyone passes on their way through town. But do you know about the rich history and modern functionality of the dam on Bridge Street? It’s a popular attraction, drawing eyes from passersby, and questions from residents and tourists alike. The history of the dam and sawmill dates back to 1855, and its evolution serves a valuable purpose today.

The dam and sawmill were constructed in 1855 to support the flour, woollen, and barley mills; the primary economic driver at that time. This was the first major business to operate in the town of Thornbury, employing many locals. The mill was rebuilt in 1877, after a fire destroyed the original, and the dam was rebuilt in 1912. From this, the Mill Pond was established, which housed the water that powered the mill. Today, the dam provides hydro-electric power for the Town of The Blue Mountains.

The most unique feature of the Thornbury dam, and the one that attracts plenty of onlookers, is its fishway. A fishway is commonly confused with a fish ladder. While the two serve similar functions, there are distinct differences. The Thornbury fishway was designed to mimic nature, assisting local fish as they swim upstream to spawn. Whereas, a fish ladder relies on the fish jumping into a series of concrete boxes that lift them up and around a dam, Thornbury’s fishway looks and feels like a natural river, with low gradient pools that propel the fish upstream.

As for native fish species, and when they’re most active, Chinook Salmon typically start their run in August, and are active thru September. Once they’ve spawned upstream however, that concludes their life cycle. Rainbow and Brown Trout on the other hand, typically run upstream in the spring to find a place to spawn. After they’ve spawned, they swim back downstream to Georgian Bay, and the cycle continues. For all species, fish are triggered by water temperatures and flow rates.

Observing the fish entering the fishway is a popular pastime, as they must jump to get in. This design is intended to deter non-jumping fish (e.g., carp, suckers, bass, etc.), from entering the fishway, and consuming valuable space and resources.

The evolution of the dam, mill and fishway over the past 160+ years is evident in not only the fishway on the east side of the bridge, but the electrical power generator on the west side. The original sawmill has been rebuilt and refurbished, and now operates as a restaurant, aptly named The Mill. Though the landscape has changed, fish behaviour remains the same. The Town has simply made it easier and more efficient for the fish to complete their spawning cycle.

A visit to Thornbury would be incomplete without a stop along Bridge Street, and if you find yourself passing by this Spring, make sure to keep an eye out for some familiar faces travelling through the fishway!

As a reminder, when enjoying a public space in The Blue Mountains, please remember to practice 2-metre physical distancing, wash your hands regularly, stay at home if you are sick and keep updated on current public health guidelines and provincial orders.

During provincial or regional stay-at-home orders, you can observe the fish in action safely from home via underwater videos, and view historical data, online.

For more information about the fishway, check out the fishway video series or visit the Town’s website.