St. Lawrence Information

Written By Robert Wood
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The St. Lawrence River forms part of the border between Canada and the USA - see atlas of the world.
It is a long river flowing from Lake Ontario through Montreal to the estuary in the province of Quebec, ending with the Island of Newfoundland.
It is a very large estuary. The water is fresh upstream of Quebec City, thus you will find yourself less buoyant than in the ocean. The estuary has mixed fresh/salt conditions which varies from place to place.
The section of river between Kingston and Montreal has been built into the St. Lawrence Seaway which takes ocean going vessels to the Great Lakes - (HOMES, remember from school?) Dams were constructed near Cornwall, flooding whole towns! There are also hydroelectric generating stations in these dams.
The Thousand Islands region of the river, at the effluence of Lake Ontario, contains many islands formed by the rock of the Canadian shield as it sweeps South to form the Addirondacks in up-state New York. This area has summer temperatures regularly into the 80s and lots of sunshine. It really is a northern river and not crowded or polluted.

The diving season, for most people, is from April/May to October.
During the winter months, the shipping channel is closed. However, the river often doesn't ice over between Kingston and Cornwall and it is therefore possible to dive in the shipping channels during the winter months.

Temperature within the river is uniform, varying throughout the season from 50F -> 75F -> 50F. From November to April, the temperature is 45F -> 32F -> 45F :)
In Lake Ontario, up to and including the Wolf Islander wreck, there is a thermocline which, at the height of the season, is at about 55'-60'. Above that, the temperature tracks that of the river; below it is a more or less constant 50F-55F during the season.

There is negligible current in Lake Ontario. In the river, current conditions can vary immensely, even from day to day for any particular site. This depends upon the amount of recent rain, storm conditions and the use of the dams in the river.
There are sites with zero current and others with strong current, > 4 knots. Famous strong current sites are Lillie Parsons, Lock 21, Daryaw and various river drifts. These make some excellent drift diving but also require some physical effort and experience.
Some wrecks with strong current, such as the Daryaw, can best be visited by drifting onto them from upstream.

Diving equipment is generally a full 6.5mm (1/4") wet suit. Hood and gloves required below 60F. Above 60F, people begin to shed hood, gloves and farmer john's (above 65F depending). Some form of glove, such as a gardening glove, is always recommended for protection against cuts from the Zebra Mussel, which are very sharp. Dry suits are quite popular in this area as it enables year round diving :)
Below 50F, many people prefer a dry suit. If a wet suit is used in these temperatures, then it is important to have somewhere sheltered from the wind after the dive to rapidly change to warm clothing.
A cold water regulator is strongly recommended for winter. Water temperatures below 40F will cause a standard regulator to free-flow.

Viz. varies from site to site but, in season, is generally between 25'-45'. There are daily variations, depending upon rain, storm, etc. Thus, Lock 21 is a notoriously bad viz. site - 15' being considered good there. I had 85' a couple of times last season but that is exceptional - and wonderful.
Also, in the lake, above the thermocline, the viz. is poor at the height of the season due to algae bloom. Below the thermocline, it is a good 30' - 45'.

Fish are pike, muskellunge, eel, carp, bass, catfish, etc. but the area is not known for its diverse and abundant life. However, it's always good to see a pike eat a fish. Water visibility has been immensely improved over the past few years by the arrival of the famous Zebra Mussel. This alien creature has forced out local fresh water mussels but not affected the rest of the critter population. It has even improved aquatic plant life, which had been affected by pollution over the years.
See the web page: Zebra Mussel Resources

There are plenty of different diving sites - wrecks, walls, drifts even submerged power stations, locks and other terrestrial structures.
Some sites are shore access but many require a boat.
Depths are typically 30'; 60'-120' and deep (i.e "tech- dive" deep).
The village of Rockport is noted for it's deep sites - Rockport Wall to 300' and the wreck of the Jodery - starts at 130' and goes to 240'.
Popular shore dives are Rothesay, Conestoga and Prescott docks (for novice and out-of-season dives); Rockport and Lock 21. Note, Lock 21, although only 60 feet max depth, is an advanced dive due to the poor viz. and strong current.
Popular boat dives are Wolf Islander, Marsh, Keystorm, Kingshorn, America, Vickery, etc.
Architectural sites include various submerged shipping locks and the old Mille Roches hydroelectric generating powerhouse.

DND Charters
Abucs Scuba, Brockville
Limestone Diving, Kingston
or 613-547-dive
Rockport Dive Centre, Jeff Pauze
Down Under, Brian Pemberton
or 514-622-3324
Kingston Dive Centre
Ron McDonald, Brockville
Dave Lockhart, Cardinal
or 613-657-1104
Suspense Charters, Kingston
Bob Dumont, Long Sault
Ross Doe, Crysler Marina
Get Wet Scuba, Gananoque
Phoenix Dive Centre, Ivy Lea
Sea N Sky Scuba, Prescott


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