Agricultural pollution comes from non-point sources, making it difficult to quantify. The intensive use of fertilizers and pesticides and erosion of farmland along the River is cause for concern for the St. Lawrence ecosystem. One-third of the River's wetlands were lost to farming between 1945 and 1976. The power generation industry has had a major impact on the environment. Hydroelectric dams cause major changes to the aquatic ecosystem, while conventional and nuclear thermal power plants require high volumes of water for cooling and their discharges increase water temperature, which can have a harmful effect on the environment.
Commercial fishing helps drive the economy of the Gasp , Magdalen Islands and Lower North Shore.
The groundfish sector is going through an unprecedented crisis, severely affecting the regional economy. This shoreline urbanization has an impact on the River in terms of wastewater discharges and encroachment. The River drives industry by supplying factories and plants with the water needed for their processes. While industry contributes to Quebec's economic growth, it also adds to the pollution of the St. Lawrence. However, the St. Lawrence Action Plan has successfully encouraged industrial clean-up, primarily through a program targeting 50 priority plants that were major polluters of the River.