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Although the use of lead ammunition for shooting wildfowl and/or over listed wetlands in the UK has been banned, c. 70% of ducks shot in England (the only UK country with compliance monitoring) are still shot with lead and the proportion of ducks found dead with signs of lead poisoning from ingested gunshot has not declined significantly since the ban. However, there is little quantitative evidence of the impacts of additional mortality from lead poisoning on duck populations. For the eight duck species that winter in freshwater habitats in the UK, we found that inter-specific variation in mean population growth rate during the period 1990/1991 to 2013/2014 was significantly negatively correlated with two independent measures of the prevalence of ingested lead gunshot in the UK and Europe. This relationship was found for a wide range of different periods over which population growth was estimated, and also for annual growth rates in the period 1966/1967 to 2013/2014, derived from smoothed population trajectories. These findings support the hypothesis that ingested lead gunshot might affect population trend. An alternative hypothesis, that migratory short-stopping driven by climate change affected trends in numbers of ducks wintering in the UK, was not supported by simple or partial correlation results. The possible impact of ingested lead gunshot on the Common Pochard Aythya ferina, a species listed as globally threatened, is of special concern.