If you live in the East Bay and you have a dog that loves a good dip in a body of water, it's hard to beat this spot next to Lake Anza in Tilden Regional Park. There is a great hike around the lake that has a trail that keeps bringing you right back to the waters edge for more opportunities for them to jump in.
For the two legged swimmers, you'll need to head toward the lakeside beach that you see and the official, roped-offed, swimming area of the lake. There are lanes for open water swimmers and of course the huge recreational space for everyone to just jump in and enjoy. On a hot summer day (which is the autumn time for those of us in the Bay Area), a dip in Lake Anza is always a good idea.