Moises Rivera and Marisol Medina had a clear vision in mind when they began their summer excursion in the mountains above blistering Los Angeles recently — and that vision definitely included a cooling dip in the East Fork of the San Gabriel River. Urged on by images like-minded urbanites have posted to YouTube, Instagram and TikTok, the couple looked forward to floating in a picturesque swimming hole where oak and sycamore trees threw shadows over clear, serene waters. Yet even before they found a place to park, Rivera, 32, and Medina, 27, were greeted by harsh, unfiltered reality. Chaotic crowds swarmed a 2½-mile stretch of river whose rocky banks were marred by graffiti. Roadsides were heaped with all manner of garbage: rotting food, barbecue grills, bottles, ice chests, soiled diapers and float toys.