Elevated arsenic levels in the west part of House Lake

On October 20, 2025, the Ministry of the Environment, Conservation and Parks (MECP) advised Public Health Sudbury & Districts that water samples collected by MECP from the west section of House Lake on August 8, 2024, had concentrations of arsenic that exceeded the Ontario Drinking Water Standards (ODWS). This location is near the abandoned McMillan Gold Mine.

MECP also shared that:

• Water samples collected from the east section of House Lake met the ODWS.
• Water flows from east to west in House Lake before flowing into Moose Lake.
• Water samples collected from Moose Lake also met the ODWS.

It is not expected that arsenic from the west end of House Lake would impact the east part of the lake, as the water flows from the eastern side to the west.

As a result, Public Health recommends that the water from the west end of House Lake not be consumed or used for food preparation unless it has been treated for arsenic. Water treatment systems are available from water treatment companies. Other options include an alternate water source or bottled water.

The risk for bathing or swimming in this water is low; however, individuals should avoid drinking the water during these activities.

With respect to fish consumption for House Lake and Moose Lake, Public Health recommends following the guidelines found in the most recent edition of the Ministry of Environment, Conservation and Parks’ Guide to Eating Ontario Sport Fish: https://www.ontario.ca/page/guide-eating-ontario-fish.

The Ministry of Energy and Mines has installed mine hazard signage at the former McMillan Mine site in the north-west area of House Lake to inform and caution visitors about potential risks in the area.  As high levels of arsenic were found in the tailings of the former McMillan Gold Mine, the Ministry of Energy and Mines, and Public Health strongly recommend staying off the tailings area.

For questions regarding arsenic and health effects, please visit our website at phsd.ca or contact Public Health Sudbury & Districts at 705.522.9200, ext. 464.

For questions regarding House Lake water sampling and the Guide to Eating Ontario Sport Fish, please contact the Ministry of Environment, Conservation and Parks at 705.564.3237

For questions regarding the former McMillan Gold Mine tailings, please contact the Ministry of Energy and Mines at 705.507.6623 or minerehab@ontario.ca.