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  • Kyle Alguire


Updated: Mar 21

This 1956 photo, situated where what is now Macdonell Island in the Long Sault Parkway Provincial Park


Looking west, upriver, of what used to be the “Long Sault Rapids”. The tower on the right sits on the outer wall (towpath) of the Old Cornwall Canal just before Lock 21 (right edge of photo). The left tower is on Long Sault Island on the U.S. side. The Cableway spans the St. Lawrence River where a new earthen cofferdam has been built.


    The St. Lawrence Seaway Project required the building of several temporary dams to allow the construction of the permanent ones and modernize shipping locks and their channels. This dam referred to as “Cofferdam E” and designed to divert the waters feeding the Long Sault Rapids. In order to expedite the cofferdam’s construction, the Cableway equipped with a massive dump bucket, was erected and used in conjunction with dump trucks and heavy earth moving equipment.

Looking north from the U.S. side shows the ferocity of the Long Sault Rapids. In behind the canal wall (towpath) is a freighter heading downstream in the Cornwall Canal after it exited from Lock 21.

Looking south as the cofferdam nears completion.

This aerial photo of the completed dam, note the freighter entering Lock 21 (in the bottom of the right corner) heading upstream.

Topographical Chart drawn by The Hydro-Electric Power Commission, 9 Nov 1955

Blue outline showing present day water levels. Green outline showing land. Yellow line is the Long Sault Parkway road. Purple line is Cableway and Tower over top of the proposed Cofferdam E. The Dive flag is the present day Lock 21 dive site. Note Canada/US boundary line down the center of the river.

   Another interesting point is the “CUT F” project appearing on the lower right. This depicts a massive channel to be cut through the Long Sault Isl. to redirect the flow from Cofferdam E, creating another island after the Inundation. It is said that this work went on 24/7 for 2 years to complete the dig.

This present day river bottom Relief Chart overlay clearly shows the remnant of the cofferdam as well as the Lock 21 dive site. The area of the Long Sault Rapids shows at the end of Macdonell Island where the river bottom starts to rise and the land narrows.

Google Maps Satellite shot.



Diving this area:

It is well known that Lock 21 has current at the top of the structures but is a very manageable dive once shielded behind its huge stone walls. Some groups will also drift the current all the way east to the end of Macdonell Isl. and exit where the pavement of Old Hwy #2 goes in the water.

**Diving The Cableway site should only be attempted with a DPV. (Diver Propulsion Vehicle) aka scooter.

   We normally set up midway at one of the many grassy “Day Use” pic-nic lots on Macdonell island (just east of the Lock 21 dive site) anywhere off the gravel road between the two submerged paved ends of Old Hwy #2. Here you’ll find a very gradual entry until the drop wall of the Old Corwall Canal. A short crossing of the 45-50’ deep canal will have you climbing up and over it’s outer wall (the old towpath) then into the boulder covered old river bed of the Long Sault Rapids. Heading south/west in the 50-70’ depth will lead you to the berm that used to be the cofferdam. Following it south will eventually reveal a couple of 2” diameter steel cables that we believe were part of the Cableway Tower anchor lines on Long Sault Island.

The pair of cables end up as a loop tied to a massive twin trunk tree stump, in approximately 30’ depth.

A blurry close-up of this photo shows 2 anchor cables to the rear of the tower, circled in yellow.

Another zoomed in photo showing the Cableway tower and a total of six anchor cables, some disappearing in the forest.

Although many stumps are present in the area, no other cables have been found underwater.



After you leave the cable loop site you can go west against the current where you encounter truck size boulders that are randomly scattered. Opting to head east with the current to an area we’ve dubbed “Stumpytown” where dozens of large tree stumps remain from the cleared and once exposed shoreline of Long Sault Isl. The swift current has exposed many of their tentacle like roots to create horror/sci-fi like movie setting, a very remarkable site to see!

   It should now be time to head back north to our exit point, this path home should be more of a westerly by N/W heading, depending how far east you ventured in Stumpytown. On the way you should encounter more SUV sized boulders, as well as a few smooth flat rock plateaus that lie in stepped layers until you reach the unmistakable steep outer wall (towpath) of the canal. Crossing the canal, up its inner north wall and then surfacing to get a bearing to tell you where to go for your exit point.

On one of our return trips from Stumpytown we stumbled on a CROSS shaped steel I-beam structure, approx. 60’ long X 5 ’ high.

We believe this may have been part of section of the Cableway tower structure from the Canadian side of the St. Lawrence River, but have been unsuccessful in locating again.

We just want to remind divers that crossing this section of the river is ALWAYS very high current, can have very poor visibility, and should be done by SOLO certified divers as you may get separated from your dive buddy.


Marc Pilon, Andrew Emard, Sam Hamed, & Jason Xenakis

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