Perhaps a mutt - part hound and part water dog would be the best. But are there any known purebreds that are good at both?
For context, by running I mean 10k+ on trails and swimming I mean 1k+ in open waters.
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Based on your response above, I'd definitely recommend a working breed and make them big so they can handle the distance elements.
Some examples might be:
A medium drive german shepherd would be perfect, enough drive to want to work/run but not to much to be switched on all the time. I have one medium drive (and one high) and she loves runs, swims and bike rides.
For swimming this is down to each individual dog some dogs just don't like water at all. One of my GSDs would live in it if possible, the other hates it. So getting the dog used to water from a young age helps in the future, playing with a hose or in a paddling pool when they're young are good ways of introducing them to water.
Also to be able to run with these types of dogs you need to let them grow and develop so you cant do any running until atleast 14 months old when they're almost fully grown. This is due to their size, because these big dogs grow so rapidly it means their joints are very sensitive to over exercise and if not looked after carefully can cause issues later in life. The recommended maximum exercise until 14 months is 5-10 mins MAX per month of age.
Also look for a good breeder which can provide documented past lineage of the pup and look for any evidence of joint issues.