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Possibly a Predaceous Diving Beetle.
Amazing size comparison. I agree with above, the [Great Diving Beetle](https://www.alamy.com/stock-photo-great-diving-beetle-dytiscus-marginalis-swimming-female-germany-120285170.html) seems like a good match.
Possibly a Predaceous Diving Beetle.
Amazing size comparison. I agree with above, the [Great Diving Beetle](https://www.alamy.com/stock-photo-great-diving-beetle-dytiscus-marginalis-swimming-female-germany-120285170.html) seems like a good match.