By Conservatoire Lac brome

Climate change is intensifying hydrological extremes, alternating between episodes of heavy rainfall and prolonged periods of drought. The year 2025 illustrated the opposite of the major high flow events observed in 2024. A long drought, from mid-July to the end of September, had noticeable effects on the lake’s water level and water quality.

The lake level remained 20 to 30 centimetres below the median from mid-August to the end of October, while low precipitation resulted in exceptionally clear water from mid-July to the end of August. Despite this, cyanobacterial blooms were still observed at several locations in October, highlighting the complexity of the dynamics at play.

Monitoring of phosphorus inputs

Since 2008, the Conservation Lac Brome (CLB) team has carried out rigorous monitoring of tributary water quality in order to identify the main sources contributing to phosphorus inputs, which accelerate the lake’s aging process. Data collected in 2025 show that these inputs originate from both natural processes and human activities.

Urban and agricultural pressures

Urbanization is exerting significant pressure, particularly in the watersheds of Pearson and Inverness creeks. Disturbance of phosphorus-rich soils and poor runoff management continue to affect water quality. CLB works to ensure that measures for sustainable stormwater management are put in place.

On the agricultural side, fertilizer spreading on cultivated lands remains a concern, especially in the areas of Quilliams and McLaughlin creeks. This pressure is further amplified by the presence of organic-matter-rich wetlands that naturally release phosphorus into the hydrological network. Collaboration with local producers therefore remains essential for CLB to reduce inputs and adapt practices.

The 2025 findings are a reminder that each creek has its own story, and that the health of Brome Lake depends on the collective efforts of all stakeholders across the territory