It's rumored that summer happens outside of San Francisco in July and August. If you are in the city and don't believe this to be true because you're zipping up your second SF fleece and shivering in the fog, don't worry. Summer is just across the Golden Gate Bridge on the Russian River in Forestville.
Sunset Beach River Park is one of the many places you'll see people setting up day camps along the river, settling in with coolers and floaties for the day.
You can get there by renting a canoe or kayak at one of the nearby outfitters or you can drive and park near the bridge. Bring only plastic containers and don't feed the ducks.