Fish die-offs are concurrent with thermal extremes in north temperate lakes


As environmental temperatures continue to rise and organisms experience novel and potentially lethal conditions1,2,3,4,5, the possibility of increased mass mortality events for animal populations appears likely1,6. Yet, due to die-off rarity and unpredictability, there have been few large-scale attempts to quantify the relationship between mass die-offs and local environmental temperatures. Here, we address this issue by analysing a database of 502 freshwater fish die-offs combined with lake-specific temperature profiles simulated for north temperate lake ecosystems. Die-offs driven by extreme summer conditions occurred disproportionately in lakes with warmer average surface temperatures and during periods of extreme heat. In contrast, we observed no relationships between current thermal extremes and die-offs attributed to infectious disease or winter environmental conditions. We forecast fish die-offs driven by summer environmental conditions to double by mid-century for north temperate lakes (2041–2059) and to increase more than fourfold by late century (2081–2099), particularly at southern latitudes. These results expose a direct link between novel temperature regimes and the increased probability of catastrophic ecological events in freshwater ecosystems.

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Fig. 1: The relationship of lake temperature to fish die-offs.
Fig. 2: The trend of summerkill events anticipated over the coming century.
Fig. 3: The historical and predicted future distribution of summerkill events.

Data availability

All data that support the findings of this study, including R scripts, are available at and will be appropriately archived following the publication of this manuscript. All demographic and environmental datasets are available from public sources as referenced.


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We thank the University of Wisconsin Department of Zoology, Wisconsin Department of Natural Resources and Reed College Department of Biology. A.T. was supported by a Reed College Stafford Post-Baccalaureate Research Fellowship. A.L.R. was partially supported by the P.B. Moyle and California Trout Endowment for cold-water fish research. L. Winslow provided access to the modelled thermal data. K. Bott provided computing support. A. Siepielski and T. Layden provided helpful comments on earlier versions of the manuscript.

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A.L.R. and S.B.F. conceived the initial study. A.T. and A.B. analysed the data. A.T. and S.B.F. wrote the first draft of the paper. All authors contributed substantially to revisions.

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Correspondence to Samuel B. Fey.

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The authors declare no competing interests.

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Peer review information: Nature Climate Change thanks Matthew Guzzo and other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–6, Supplementary Table 1 and Supplementary References.

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Till, A., Rypel, A.L., Bray, A. et al. Fish die-offs are concurrent with thermal extremes in north temperate lakes. Nat. Clim. Chang. 9, 637–641 (2019).

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