It still quite hot in LA (about +30 - +33 degrees in a day time). It doesn't help to water temperature. It's cold for swimming (+18 - +20). Once you've entered in the water, it's already time to start think about exit. Still you have a nice view.
Here are Santa-Monica beaches. Just next to Malibu (yes, exactely the Malibu where Baywatch was filmed). From this place ocean looks amazing, though such sand seaside not through the whole west coast.
Santa Monica is famous not only cause its beaches, but also the famous route 66 ends here. It is also call "The Mother Road". It is one of the first route in USA. 3490km from Chicago to western coast.
There is not really much you can do in LA. I had an impression of a dirty city. They have some special sightseeing places in the city worth to visit. Well, just to check elite districts like Mullholland drive and Beverly Hills. It's really extremely picturesque view from there.