Walking a pup isn't hard on it's hips, as long as the pup isn't genetically predisposed to Hip Dysplasia.
And if it is genetically predisposed to Hip Dysplasia, it's going to develop Degenerative Joint Disease no matter what you do.
Instead of worrying about what activities might be too physically demanding of a pup, it's better to always be cognizant of how much fun the pup is having. And always stop, while the pup is wanting more.
No matter what activity you are engaging in as play, (and play is all that a pup is capable of) consistently doing it until the pup loses interest and quits, is teaching the pup to hate that activity.
Keep nature walks short.
Keep retrieving sessions short.
Keep rides in the truck/boat short.
Keep swimming lessons short.
Make sure that you get the pup excited and happy during the sessions, try to improve on the behavior with each session, and always quit before the pup starts to become bored.
That's how you develop a pup's attitude about training, water, and retrieving.
To a puppy, five minutes is a long time. They can go from bouncing-off-the-walls-happy, to snoring-ass-bored in five minutes.