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Ottawa Divers blog on adjacent Lock 21 conditions, providing regional current and visibility context
Dive Spot Guide•
Lock 20
Submerged 1958 Cornwall Canal lock with stone masonry chambers and weir.
Shore dive near Cornwall, Ontario with river current variable; site near the hydroelectric barrage requires experience and pre-dive planning.
About Lock 20
Lock 20 is a submerged section of the historic Cornwall Canal, flooded in 1958 during construction of the St. Lawrence Seaway. The site preserves a 270-foot stone lock chamber alongside an earlier 200-foot lock and weir structure, now resting on the river bottom near Maple Grove. Divers trace the hand-cut limestone masonry of the lock walls, wooden gate remnants, and the weir apron in relatively sheltered freshwater conditions. River current and proximity to the Cornwall hydroelectric barrage mean conditions vary, and dives here require familiarity with the site layout, rope navigation, and exit planning before entry.
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Research Estimate At Lock 20
Conservative baseline from public research. No community dives logged yet.
VisibilityVisibility: 6m
AccessModerate entry effort
Aquatic LifeSome life
FacilitiesLimited facilities
CurrentModerate current
Where Is Lock 20?
This spotNearby spotsExplore nearby spots on the map
Community sourced coordinates.
Lock 20 Planning Details
Depth range, seasonality, and planning context.
Reported Depth
5m - 15m
Depth Note
Canal lock sill was 14 ft deep at construction; 1958 flooding raised water level above the structure. Actual dive depth over the lock chambers is shallow to moderate. Reviewer should verify with local operator — no explicit depth measurement found for Lock 20 specifically.
Best Season
Late spring through early fall (May to October) is the typical dive season. Water is coldest in spring and clearest after summer thermocline stabilizes.
Typical Conditions
Freshwater dive with variable visibility (generally 3-10 m in good conditions). River current from the barrage upstream can vary from mild to strong. Water temperature ranges from 8-22°C seasonally.
Safety & Access At Lock 20
Hazards, restrictions, and access requirements.
Key Hazards
Boat trafficLow visibilityStrong current
Safety Notes
River current from the upstream barrage is the primary hazard; strength varies and is not always predictable. Attach to guide ropes where available and plan exit points before entry. Boat traffic from the St. Lawrence shipping corridor is active in season. Visibility can drop significantly with water conditions.
Access Restrictions
Access via the Long Sault Parkway area requires a St. Lawrence Parks Commission entry fee during the operating season. Confirm access points with local operators before visiting.
Legal Notes
The Long Sault Parkway is managed by the St. Lawrence Parks Commission; season fees apply. No specific permits required for recreational diving beyond parkway entry, but check current regulations with the Commission.
Local Intel For Lock 20
Community notes to help plan your visit.
Scuba Diving
Route follows the lock chamber walls from the entry point along the 270-foot lock, exploring stonework and wooden structural remnants. The old 200-foot lock chamber and weir offer secondary exploration. Rope navigation is advisable given current variability. Exit planning is essential given the current direction.
Wildlife at Lock 20
Species commonly reported at this site, with direct links into their wildlife guides.
Recent Logged Visits At Lock 20
Community dive logs and visit reports for this site.
Dive Spot Log Averages At Lock 20
Average conditions based on logged dives & visits.
Conditions
Avg. Visibility6m
Activity
No dive activity logged yet.
