ADDENDUM: The expedition returned Aug. 23, 2015 to the San Francisco Bay. Researchers report that much of the plastic collected on the expedition was dumped in the 1950s and '60s. Watch this report.
The Ocean Cleanup project's Mega Expedition, billed as "the largest expedition in history," has about 30 vessels sailing from Hawaii to Los Angeles. In the end, researchers hope to cover 3,500,000 km2 in an effort to collect more measurements of the mass of the Great Pacific Garbage Patch. Visit The Ocean Cleanup project's website for live updates.