Is swimming limited to a specific date/season, or is it up to the visitor?

Up to you

You can swim anytime but the water is cold.

Feel free to roam about the park and partake in whichever activity you desire or can stand

I think it's up to you, but I don't know how cold the river is right now.

Can I see the campsites

All above answers combined are correct. You have to stay out of restricted areas. Water will be cold to cool. Very nice park.

You can swim anytime but no life guards and there are some restricted dangerous areas. Look for the signs.