Led by the Bay Foundation, divers in the Santa Monica Bay have spent 15,575 hours underwater over the past 13 years. To bring the kelp back, they focus on minimizing the impact of one voracious eater: the purple urchin. The effort has been successful, smashing 5.8 million purple urchins and clearing 80.7 acres (32.7 hectares, the size of 61 football fields), and allowing the kelp to return.