Widespread occurrence of in Ontario, Canada, and predicted habitat suitability for the emerging .

Chytridiomycosis, caused by the fungi and , is associated with massive amphibian mortality events worldwide and with some species' extinctions. Previous ecological niche models suggest that . is not well-suited to northern, temperate climates, but these predictions have often relied on datasets in which northern latitudes are underrepresented. Recent northern detections of . suggest that these models may have underestimated the suitability of higher latitudes for this fungus. We used qPCR to test for . in 1,041 non-invasive epithelial swab samples from 18 species of amphibians collected across 735,345 km in Ontario and Akimiski Island (Nunavut), Canada. We detected the pathogen in 113 samples (10.9%) from 11 species. Only one specimen exhibited potential clinical signs of disease. We used these data to produce six Species Distribution Models of . , which classified half of the study area as potential habitat for the fungus. We also tested each sample for . , an emerging pathogen that is causing alarming declines in European salamanders, but is not yet detected in North America. We did not detect . in any of the samples, providing a baseline for future surveillance. We assessed the potential risk of future introduction by comparing salamander richness to temperature-dependent mortality, predicted by a previous exposure study. Areas with the highest species diversity and predicted mortality risk extended 60,530 km across southern Ontario, highlighting the potential threat . poses to northern Nearctic amphibians. Preventing initial introduction will require coordinated, transboundary regulation of trade in amphibians (including frogs that can carry and disperse . ), and surveillance of the pathways of introduction (e.g., water and wildlife). Our results can inform surveillance for both pathogens and efforts to mitigate the spread of chytridiomycosis through wild populations.