Effluent is the treated liquid waste discharged from wastewater treatment plants into receiving waters like rivers, lakes, or oceans. Before discharge, wastewater undergoes multiple treatment stages to remove solids, organic matter, nutrients, and pathogens to meet environmental standards. Effluent quality is regulated by provincial and federal environmental authorities who set limits on contaminants like phosphorus, nitrogen, suspended solids, and bacteria. Treatment plants regularly test effluent to ensure compliance. While modern treatment produces relatively clean effluent, it's not pure water—it still contains some pollutants that can affect receiving waters, particularly when volumes are large or receiving waters are already stressed. Municipalities invest heavily in treatment upgrades to meet increasingly stringent effluent standards, with climate change adding pressure as extreme weather affects both treatment processes and receiving water conditions.