Looking for lake vacation ideas

I am looking for updated recommendations for places we can vacation this summer where we can swim in a lake. We have a preschooler, so ideally, it would have a nice beach to play on, and easy hikes nearby. I'd love to standup paddle, but otherwise we don't need a lot of activities. We would like to rent a cabin (or house), though I'd welcome recommendations for charming hotels/lodges as well. 

We are focusing our search on Northern CA and Oregon and would prefer not to go too far south to avoid really warm days. 

Thanks for your help!