A long-term monitoring dataset of non-breeding waterbirds at Lake Miedwie, Poland (2002–2025)

This dataset presents waterbird count data collected during the non-breeding season from 2002/2003 to 2024/2025, covering 23 seasons across 24 calendar years. The dataset includes 952 records of seasonal abundance for 14 waterbird species. The average total abundance was 7,933 (± 1,314 SE) individuals per season (mean of November, January and March), with a maximum of 36,095 in November 2002 and a minimum of 226 in March 2017. Trend analysis using the rtrim package in R indicated a moderate overall decline (λ = 0.976, 95% CI: [0.975 - 0.977]). Species-specific trends varied, with some taxa, such as Greylag Goose (<i>Anseranser</i> Linnaeus, 1758), increasing, while others, including Greater White-fronted Goose (<i>Anseralbifrons</i> Scopoli, 1769), Eurasian Teal (<i>Anascrecca</i> Linnaeus, 1758) and Eurasian Coot (<i>Fulicaatra</i> Linnaeus, 1758), declined. The dataset contributes valuable baseline data for wetland bird conservation, ecological assessment and future research in Central Europe. Importantly, such long-term monitoring also provides a robust reference point for assessing changes in climate and biodiversity over time.