This study provides a unique opportunity to realistically assess the impact of tourism pressure on the water quality of lakes. A quantitative analysis of the physicochemical and microbiological parameters of water during and after the COVID-19 lockdown period was made. The study covered Sztynorckie Lake located in the Great Masurian Lakes System (GMLS) (northeastern Poland), which is a holiday destination for hundreds of thousands of holidaymakers, and serves as a pillar of the local economy. Significant improvement in the microbiological water quality was observed only during the drastic reduction of human activity due to the pandemic-enforced lockdown. This was confirmed by the results of PCA (X-axis explains 88 % of the variability of the analyzed samples; statistical significance of p<0.05). The rapid increase in the number of coliforms and Escherichia coli (613.1 MPN/100 mL) in the first weekend after the lockdown (June 2020) indicates a point discharge of sewage (including fecal pollution). Illegal discharge of sewage and wastewater is a highly reprehensible offense, and radical legal steps should be taken to prevent it and to protect the water quality. No significant relationship was found between the lockdown and the lake water's physicochemical conditions. In the spring, increased primary production was evidenced by the high concentration of chlorophyll a (52.5 to 70.5 μg/L), suspended particulate matter (20.4 to 21.0 mg/L) and total organic carbon (20.7 to 22.7 mg/L). This is a warning that a nutrient-rich lacustrine ecosystem cannot be restored quickly.

这项研究提供了一个独特的机会来现实评估旅游压力对湖泊水质的影响。对 COVID-19 封锁期间和之后水的物理化学和微生物参数进行了定量分析。该研究涵盖了位于大马祖里湖区系统（GMLS）（波兰东北部）的斯蒂诺基湖，该湖是数十万度假者的度假胜地，也是当地经济的支柱。仅在由于大流行强制封锁导致人类活动急剧减少期间，微生物水质才出现显着改善。PCA 结果证实了这一点（X 轴解释了分析样本的 88% 变异性；p <0.05 的统计显着性）。封城后第一个周末（2020年6月）大肠菌群和大肠杆菌数量迅速增加（613.1 MPN/100 mL），表明存在污水（包括粪便污染）点排放。非法排放污水和废水是一种应受严厉谴责的犯罪行为，应采取彻底的法律措施来防止这种行为并保护水质。没有发现封锁与湖水理化条件之间存在显着关系。春季，初级生产力的增加表现为高浓度的叶绿素a（52.5至70.5微克/升）、悬浮颗粒物（20.4至21.0毫克/升）和总有机碳（20.7至22.7毫克/升）。这是对营养丰富的湖泊生态系统无法快速恢复的警告。