The one and only outlet of Lake Tahoe is the Truckee river. Even though you can only go rafting in certain sections and during periods where the water level is high enough (drought season has been hard on Tahoe lately), you can float down the river for a few hours and enjoy the natural serenity and sun shine.
Equipment: You can pick up rafts, paddles, inner tubes, etc in Tahoe City and in the summer, there is a stand right at the drop-in point.
Stand up paddling has become quite popular at Lake Tahoe. If you haven't tried it yet, this is a very good place to learn. The water usually isn't as challenging as the ocean, and it's so clean. I'm used to paddling in salt water, estuaries and sloughs (some of it rather brackish and containing silt) since I live near the beach, so it is quite a treat to paddle in clear, clean water where I can see the boulders 20 feet beneath the paddleboard.
For the more advanced, Lake Tahoe is a popular spot for SUP races. It's also so big that you can venture quite far from shore. You're not fenced in by a tiny pond. The ski boats whizzing by add some variety and challenge with their wakes. You might even be able to catch a wake.
Equipment: There are a couple of places at Kings Beach that rent SUP boards. I like Adrift because they are right on the beach, and they have a pretty decent selection of boards to try. Go early on the weekends. On a nice day, all the boards may be out by 10:00 am.