As extreme climatic events, such as heatwaves and storms, become more frequent in response to changing climates, understanding the role climatic events play on water quality is essential. Here, we use water quality monitoring data collected from the nearshore of Lake Ontario between 2000 and 2018 to ask: i) which sites in the nearshore of Lake Ontario have statistically extreme water quality conditions?; ii) do water quality conditions differ in extreme versus non-extreme climate years?; and iii) what are the significant antecedent extreme weather drivers of water quality in the nearshore of Lake Ontario? Three sites with the highest chlorophyll a concentrations and eutrophic conditions, two of which are in Areas of Concern, exhibited the strongest responses to climate extremes. Antecedent weather conditions explained 87.2% of the variation in extreme chlorophyll a concentrations. In particular, warmer temperatures and heatwaves corresponded with statistical extremes in chlorophyll a concentrations. Precipitation accounted for 35.5% of the variation in extreme conditions of turbidity, including storm events the day prior to sampling. When considering site-specific extreme conditions, antecedent weather conditions explained 66.8% of the variation in turbidity. We illustrate the strong role that heatwaves and storm events play on spatial and temporal patterns in extreme water quality conditions, highlighting the importance of incorporating climate change adaptation plans into ecosystem management strategies to preserve water quality in the highly important and iconic nearshore regions of the Laurentian Great Lakes.

随着极端气候事件（如热浪和风暴）因气候变化而变得更加频繁，了解气候事件对水质的影响至关重要。在这里，我们使用 2000 年至 2018 年间从安大略湖近岸收集的水质监测数据来询问：i) 安大略湖近岸的哪些地点在统计上具有极端的水质条件？ii) 极端气候年份和非极端气候年份的水质条件是否不同？iii) 安大略湖近岸水质的重要前期极端天气驱动因素是什么？叶绿素a最高的三个位点浓度和富营养化条件，其中两个处于关注区域，对极端气候表现出最强的反应。先前的天气条件解释了极端叶绿素a浓度变化的 87.2%。特别是，较高的温度和热浪与叶绿素a浓度的统计极端值相对应。降水占极端浊度变化的 35.5%，包括采样前一天的风暴事件。在考虑特定地点的极端条件时，先前的天气条件解释了 66.8% 的浊度变化。我们说明了热浪和风暴事件在极端水质条件下对空间和时间模式的重要作用，强调了将气候变化适应计划纳入生态系统管理战略的重要性，以保护劳伦森非常重要和标志性的近岸地区的水质五大湖。