Lock 21 is a fairly high current dive so should only be done by advanced divers who are comfortable with higher current dives. It is located off the south-western end of Macdonell Island near Long Sault.

Web information sources:

• SOS provides a great description and sketch of the lock: https://saveontarioshipwrecks.ca/diverguides/lock-21/
• Neptune: https://www.neptune-scuba.info/ca/on/ecluse-lock-21-en.html
• New York Times article: https://davidgibbins.com/journal/2016/4/8/diving-lock-21-a-submerged-victorian-canal-lock-on-the-st-lawrence-river-canada

Location: Lock 21 is located off the south-western end of Macdonell Island. From highway 401, take exit 778 toward Long Sault. Take the South direction on Moulinette Road up to Highway 2 (also known as King’s Highway). Continue heading South direction on Moulinette Road crossing Highway 2 toward Long Sault Parkway. Follow the route toward McDonell Island (2nd island)stop at the beech are of the 1st Island, Mille Roches Island to purchase a $10 dive pass, then continue to McDonell Island. After driving half way across McDonell Island, take the 2nd gravel road to the left. It will go only for about 40 meters then turn right to travel toward the West direction. It will end in about 60 meters. There is a brown pavilion where information is available about the dive site and an historic tour relating the story of the Lost Villages after the construction of the St.Lawrence Seaway. The Lock is located on the South side of the island on the St.Lawrence lake (not the St.Lawrence River which is located on the other side of the islands on the American side of the border). The GPS location is: 44°59’55.0″N 74°53’57.4″W (44.998611, -74.899270)

If you happen to drive along the Long Sault series of islands from the west end, stop at the 1st island, McLaren Island camping area and purchase the $10 diving pass from the small shop by the parking lot, then carry on to McDonell Island.