NATURE’S BEST: Frank Robinson shudders to think some folks wanted to turn Upper Newport Bay into a marina. He’s been giving walking tours of the wetlands for almost 30 years. . . . “It’s the closest thing we have in this county to an actual estuary,” he says. Friends of Newport Bay began their monthly tours in October. The next one is Saturday at 9 a.m. Robinson promises you’ll see numerous endangered species on a 3/4-mile walk. Suggestion: Bring binoculars.