Problems

Each year, thousand of commercial ships travel along the St. Lawrence—from container ships to bulk carriers loaded with ore and grain to oil tankers. These include domestic Canadian and U.S. carriers navigating between ports along the river system, as well as the ocean liners that link ports on the St. Lawrence to ports on other continents. The St. Lawrence plays a key role in the economic development of Quebec, Canada and the United States.

This heavy traffic on the river increases the risk of accidental water pollution when cargo or fuel is lost in a grounding or collision. Water quality can also be adversely affected by normal navigational activities.

When large commercial ships pass along the shipping channel, their wakes contribute to shoreline erosion. This has a particularly severe impact on the islands in the Lake Saint-Pierre Archipelago that lie alongside the shipping channel.

The eroded soil remains suspended in the water, increasing its turbidity. These sediments can also carry pollutants that further degrade water quality.

Pleasure boating can also degrade water quality. Wave action from smaller boats passing too close to land can further erode shorelines.

The waves produced by pleasure craft have a stronger effect on shorelines in narrower channels. Large numbers of small boats speeding through a small channel can significantly erode its banks.

Moving water and ice naturally erode shorelines, weakening trees growing along the banks by exposing their roots.

Boats passing near these shorelines accelerate erosion. Eventually, the trees fall down, leaving a hole in the soil that allows water to infiltrate. This contributes to further erosion.

Growing maritime traffic and the presence of larger ships increase the risk of collision when vessels meet in the narrow, shallow channel. Larger ships are difficult to maneuver, making them more likely to be involved in an accident. If a ship is grounded or collides with another vessel, it may lose cargo or fuel. An oil spill in the St. Lawrence would be extremely harmful, as the oil would be very difficult to clean up. What's more, many people live along the St. Lawrence and many communities get their drinking water from the river. Fortunately, such incidents are rare, as the ships are guided by highly skilled pilots.

Even if no accidents occur, some pollutants do leak from vessels during normal operations. These include diesel, fuel oil, heavy oil and lubricant. The harmful effects of these contaminants are felt most strongly in ports.

The waters of the St. Lawrence can also be contaminated by sewage discharged from ships and pleasure craft. Canada has adopted regulations to prevent this type of pollution, requiring vessels to be fitted with a holding tank or marine sanitation device.

During loading and unloading operations, cargo residue remains in the holds. The holds must therefore be washed out before a new type of cargo can be loaded. The washing water is then discharged into the river. Although this water contains very low concentrations of residue, deposits can build up over time and damage the environment.

Dredging operations must comply with strict environmental regulations. Each time the bottom is dredged, sediments loaded with contaminants are stirred back into the water column. These operations must therefore be strictly controlled to minimize damage to the aquatic environment.