Not 100% sure of the how and why of it, but the delta stays pretty constant other than tide. Maybe it's relatively low altitude and it's relation to the ocean has something to do with keeping it "full".
The Delta is an adventure you'll not soon forget. You could boat for days, months, or a life time and see something new every time out.
There are many good launches off of I-5. Which one you choose is up to you and may depend on what portion of the delta you want to explore.
The two that come to mind are Paradise Point off of 8 Mile Road in Stockton and B&W Resort off of Hwy 12 in Isleton. But there are more than one could keep track of. Seven Crown Resorts Paradise Point Marina B & W Resort & Marina
Go on line and order a map. Familiarize yourself. Plot a route. Note and mark stops with gas and/or food. Wouldn't be a bad idea to have your "navigator" get familiar with it too. And there's a good chance you may be able to meet up with some "native" folks to show you around a bit too.
When you're getting close to planning a trip, scroll down to the "dlb Delta Lunch Bunch" in the Clubs and Groups section of the forum, and introduce yourself. Or do it now. Plenty of good people will be happy to recommend a route, stops along the way, and things & places you should see/go.
Lastly, it's a river. Things change and there are hazards. Don't want to scare ya off, but do bring a spare prop just in case
A bit of advice, right off- Get a couple of maps of the delta....You can easily get lost- be patient and mark where you've been and where you're going and you shouldn't have any trouble; I grew up going to the delta every weekend(60s & 70s) and we basically went Grant line up to Sucide beach outside of Disco bay- After 20 years I picked up a boat and started going out there again...My friends would ask, "How the hell do you know where you're going?!" "See that tree, and the way the river curves and opens up?" I didn't get it- until we decided to go up to Franks tract- cripes, I felt like I was lost the whole time.....So- MAPS! And I suppose your phone has GPS, too.