The hook
A five-mile lake folded into the golden hills south of Livermore — the East Bay's best swimming water, and the back door into its biggest wilderness.
01Why it's worth it
Del Valle is the East Bay park system doing what it does best without any landmark to sell: a long reservoir in classic oak-savanna-and-gray-pine country where the day is the point — swim beaches with lifeguards in season, boats put-putting a 10-mph limit, eagles in the snags, and a big, happy, multigenerational picnic scene locals describe with affection ("beautiful scenery of oak savannah and gray pines, lots of big Mexican families having fun — really felt like a getaway"). Cows graze the surrounding hills close enough to make acquaintance. For the ambitious it's also the eastern trailhead of the Ohlone Wilderness Trail — 28 miles over the East Bay's highest, emptiest country to Sunol and Mission Peak, with backpack camps en route — which means you can leave the swimmers behind and be alone in twenty minutes of climbing.
02How to experience it
Del Valle Rd south of Livermore (parking + potential summer entry lines; arrive before 10 on hot weekends). East-shore beaches for swimming, rental kayaks at the marina, campground for the easy overnight. Ohlone Trail permits at the entrance kiosk if you're walking into the big country. Pairs with a Livermore-valley winery stop on the way home.