I used to have a Golden Retriever who would wallow in muddy puddles, i laughted about it for the first couple of years after that it was ''oh Holly how could you'', but she was a retriever and she was attracted to water the same as a lab.
I've got one of those, too. Sadly Bear will insist on hooning up the muddy farm track that runs alongside the road (single track road, little used)on our way home, having bathed in aforementioned stream! However, he always manages to arrive home wet, caked in mud and with a similar expression to that of the lab in the pic!