Chloride is a naturally occurring ion found in most water bodies, but concentrations rise significantly from road salt, water softeners, agricultural runoff, and industrial discharge. The Canadian Council of Ministers of the Environment (CCME) sets a long-term freshwater guideline of 120 mg/L to protect aquatic ecosystem structure and function during indefinite exposure, and a short-term guideline of 640 mg/L to protect most species against lethality during brief but severe events. The long-term guideline may not be protective enough for certain freshwater species, including endangered freshwater mussels, including the wavy-rayed lampmussel and the northern riffleshell, both found in southwestern Ontario waterways. Chloride doesn't break down or disappear once it enters a waterway, and even moderate increases can stress the sensitive invertebrates, fish, and plants that freshwater ecosystems depend on. At higher concentrations, it disrupts the ability of aquatic organisms to regulate water and salt in their bodies, which can be fatal.