Right now water in California is fast and cold. Sierra rivers fed by snow melt are killing people.
Many of the languid pools you've read about in hiking guides or seen on social media are currently unsafe for swimming. Do not make decisions about safety of a spot based on past experience. Just because you did it before does not mean you can do it this year.
This website is working to provide near realtime data for critical indicators as well as special advisories and forecasts so you can more effectively plan your trip. Until those metrics are available, use this simple rule:
When you get to the swimming hole toss a twig into the middle of the pool. If it moves more than six feet during the time it takes you to remove your shorts and shirt, water velocity may be a hazzard.