The Problem With Phosphorus
Phosphorus (P) was a common additive in lawn and garden fertilizers. It is a limiting nutrient in lakes. In excess, it can lead to eutrophication , with dense growth of algae and aquatic plants leading to decreases in water oxygen levels, harm to aquatic animals and overall decline in water quality and esthetic appeal. Urbanization of the watershed over the past ~30 years has resulted in an ongoing increase in surface (e.g. lawn) and storm system runoff. Years of development has produced a deep layer of sediment build-up. Previously bound phosphorus is now being released into Nepahwin Lake, and has led to concerning levels of phosphorus in the water.
The provincial water quality objective for P is <20ug/L.
Nepahwin Lake Phosphorus Level in 2020: 19.2ug/L 
On April 1, 2012, the Lawn Fertilizer By-Law was enacted by the City of Greater Sudbury (CGS). It restricts the use of lawn fertilizers containing phosphorus within CGS for routine lawn care. Despite the by-law, Nepahwin Lake phosphorus levels continued to rise and spiked in 2017 at 20.4 ug/L!
CGS commissioned the Nepahwin Lake Causation Study (NLCS) to address the statistically significant increase in total P in recent years. In 2018, CGS increased the frequency and scope of Nepahwin Lake water quality monitoring and in response to NLCS recommendations, will continue to do so in collaboration with NLWSG. View the full NLCS report here.
 Eutrophication Process Explainer:
1.Technical Support Document for Ontario Drinking Water Standards, Objectives and Guidelines. June 2003, rev June 2006. Government of Ontario.
2. City of Greater Sudbury. 2019. Lake Nepahwin Water Quality Summary Report
3. City of Greater Sudbury Lake Water Quality Program, 2020 levels.