Update on Moira Lake Heavy Metal Water Monitoring Results
The Ministry of the Environment, Conservation and Parks (MECP) has recently provided the 2023–2025 Moira Lake monitoring results under the Deloro Site Cleanup Project. The results confirm that water quality indicators at the monitored locations remain consistent with long-term patterns previously observed in the Moira River watershed.
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Results from the Moira River Inlet and Stoney Point Island sampling locations show:
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Most metals remain at or below Provincial Water Quality Objectives.
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No new or emerging contamination trends have been identified.
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As in previous monitoring, arsenic concentrations exceed the interim Provincial Water Quality Objective that applies to this watershed. However, concentrations remain within the historical range of values and are well below the provincial recreational screening reference concentration used to assess swimming exposure.
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MECP also notes that Level 3 drought conditions during much of 2025 may have contributed to slightly elevated concentrations observed last summer.
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For more information specific to Moira Lake, please click the Moira Lake button below.
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The MLPOA will continue to support ongoing monitoring efforts and share updates with members as information becomes available.
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MLPOA volunteers have supported this monitoring program for several years by collecting mid-lake samples in partnership with the Province. This collaboration helps maintain a long-term record of water quality data for Moira Lake and supports responsible lake stewardship.
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For additional information about the broader Deloro monitoring program, please click the Deloro button below.
Moira Lake 2025 Final Water Quality Report
May - October 2025 Summary
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Between May and October 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
The 2025 monitoring season provided the clearest picture yet of how Moira Lake changes through the year — from the clear, cool conditions of spring to a dense midsummer algal bloom and the recovery that followed in fall. Sampling across six permanent sites captured the lake’s full cycle and revealed both its resilience and its growing vulnerability.
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Phosphorus remains the main driver of algal blooms. Levels exceeded the Provincial Water Quality Objective (0.02 mg/L) across all sites, peaking in July and August at five to ten times the target.
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Hardwater chemistry (high calcium and magnesium) traps nutrients in the lake, slowing recovery and sustaining summer stress.
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Oxygen and clarity rebounded in October, showing the lake’s ability to recover when conditions cool and mix.
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Moira Lake ranked among the most nutrient-enriched lakes in Eastern Ontario, confirming it as a regional outlier that needs ongoing management attention.
Why It Matters
Moira Lake is not in crisis, but it is under increasing pressure. Nutrients and minerals build up year after year, fuelling predictable summer blooms and oxygen stress. Without action, these cycles will continue, gradually reducing water clarity, habitat quality, and recreational value.​​
2025 Summary Scorecard
What It Means
These patterns are consistent with the natural rhythm of a productive lake — but they also underscore how vulnerable Moira Lake is to nutrient input, sediment disturbance, and rising temperatures. If these trends repeat year after year, they could lead to long-term ecological shifts that are harder to reverse.
How You Can Help
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Pump out and inspect your septic system regularly
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Avoid fertilizer use near the lake
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Maintain or restore natural shoreline vegetation
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Report unusual algae blooms or fish behaviour
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Stay informed through MLPOA reports and updates
Moira Lake remains a living, responsive system — one that can still recover if given relief. With continued monitoring, community action, and strong local partnerships, lasting improvement is within reach.
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Want to Learn More?
Two documents are available for your further reading:
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A brief summary of the full report ( 7 pages).
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The full 2025 Water Quality Report includes benchmark scores, site-by-site results, detailed seasonal observations, and parameter definitions (27 page report plus Appendices, total 46 pages).