OAHU'S HANAUMA BAY
Striped Hawaiian sergeants, lei triggerfish, and green bird wrasses dart among the coral reefs at Hanauma Bay Nature Preserve, a popular snorkeling spot on Oahu's South Shore. The bay—formed when the ocean flooded an ancient volcano crater—offers a curving beach, crystalline waters, and a reef that's lively with some 150 species of colorful fish. To protect the pristine marine ecosystem, about 10 miles east of Waikiki, the Honolulu Parks Department lets a limited number of visitors into the preserve. Arrive early to beat the crowds. Admission is $5; snorkel rentals start at $6. Hours: Wed.–Mon. 6 a.m.–7 p.m. (808) 396–4229, www.hanaumabayhawaii.org.

MONTEREY BAY AQUARIUM
This is your last chance to touch a baby shark or see a four–foot scalloped hammerhead. SHARKS: MYTH AND MYSTERY ends its run at California's Monterey Bay Aquarium on September 4. (831) 648–4888, www.montereybayaquarium.org.

BONNEVILLE DAM
Underwater viewing windows at the Bonneville Lock and Dam Visitor Center in Cascade Locks, Ore., showcase migrating salmon as they swim up a fish ladder on the Columbia River. (541) 374–8820, www.nwp.usace.army.mil/op/b.