Moira Lake Interim Water Quality Report

May - July 2025 Summary

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Between May and July 2025, volunteers with the Moira Lake Property Owners Association (MLPOA) monitored water quality at six sites across the lake. This work helps us better understand how conditions change throughout the season — and what those changes might mean for the lake’s long-term health.

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What We Observed

 

Moira Lake, like many shallow lakes in Ontario, goes through seasonal changes that affect its chemistry and ecology. Sunlight, heat, and lower water movement can all influence algae growth, aquatic plants, and nutrient cycling.

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May to July results revealed a pattern of mid-summer stress:

• Phosphorus and organic material increased steadily, reaching high levels at several sites in July — conditions that support algae blooms and thick aquatic plant growth.

• Ammonia, which was elevated in spring, declined by July — not due to improved inputs, but likely because it was taken up rapidly by fast-growing vegetation and algae.

• Total Organic Carbon (TOC) reached concern levels at all sites in July, signaling a high load of decomposing plant material in the water.

• Water clarity declined at most sites.

• pH, temperature, and conductivity were elevated across the lake by July — conditions that can amplify nutrient impacts and biological stress.

 

Taken together, these results suggest that the lake’s resilience declines as summer progresses. Water quality shifts from stable in May to visibly and chemically stressed by July, especially in areas influenced by runoff and nutrient loading.