A recent study of the Saint Lawrence River, which flows through Canada and borders the city of Montreal, has found a wide range of pharmaceutical residues in its waters. Between 2017 and 2021, researchers collected over 400 water samples from a 700-kilometer stretch of the river. The analysis detected residues from substances like caffeine, diclofenac (a painkiller), venlafaxine (an antidepressant), carbamazepine (used for epilepsy), acebutolol (a heart medication), chemotherapy drugs, and various antibiotics. Four of these substances—caffeine, carbamazepine, diclofenac, and ibuprofen—were found in concentrations that could potentially harm the growth and reproduction of aquatic organisms. However, there are currently no Canadian environmental standards in place to regulate or limit these substances in waterways. Montreal, with a population of about two million, is the main source of these pharmaceutical residues. The city’s wastewater treatment plant processes nearly 900 billion liters of water each year, and contaminants from the plant have been detected as far as Lake Saint-Pierre, 70 kilometers downstream. The study was conducted by researchers from the University of Montreal, who emphasized the long-term effects of pharmaceuticals on the river’s ecosystem. Pharmaceuticals typically break down quickly in water, but carbamazepine is an exception, as it remains in the environment for longer periods. The study highlights the risk that chronic exposure to low levels of these substances poses to aquatic life, especially young fish and other vulnerable species. In response, Montreal plans to introduce ozone technology into its wastewater treatment system. This method can remove up to 80% of pharmaceuticals present in the treated water, offering a potential solution to reduce contamination. Similar issues have been observed in other parts of the world, including Europe and Australia. In some rivers in Suffolk, England, traces of drugs such as cocaine, ketamine, Valium, Xanax, and tramadol have been found in freshwater shrimp. These substances were traced back to human urine, showing that pharmaceutical contamination is a global concern. The findings emphasize the need for more effective water treatment and regulation to protect aquatic ecosystems worldwide.