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The global effort to stop plastic from choking our oceans is under attack Nov. 8. Proposition 67 on California’s ballot would ban giveaways of single-use plastic shopping bags throughout our state, not just in individual coastal and Bay Area cities. The result will either boost the movement for bans throughout the United States, or crush progress here and around the world.

Plastic bag manufacturers are going for the kill right now, desperate to protect their profits from making throwaway items. When Gov. Jerry Brown signed a 2014 law banning these bags statewide, bag makers paid signature gatherers hundreds of thousands of dollars for a referendum that blocks the law unless Proposition 67 passes. Now they’re preparing to spend millions more to confuse voters.

Novolex and three other out-of-state plastic bag makers know that populous California is not only a huge market, but a trendsetter. If they defeat Proposition 67, they deter other states and countries from banning bags, and global plastic pollution continues to grow. If we pass Proposition 67, we keep billions of plastic bags from trashing our neighborhoods, creeks, bays and beaches, and we encourage other states and countries to do the same.

Single-use plastic shopping bags create some of the most visible litter in our communities and they harm and kill wildlife every day. In our oceans, sea turtles, otters, seals, fish and birds are tangled in plastic bags. Many animals mistake bags for food, fill their stomachs with plastic bits and die of starvation. Bag pollution also costs our state and local communities $107 million dollars annually for litter cleanup. Less than 5 percent of plastic bags in California are recycled.

In the 150 California cities and counties that have banned single-use plastic bags, these laws have already proven successful. Shoppers quickly adjust to bringing reusable bags to stores, and communities see deep reductions in plastic bags clogging creeks and storm drains. San Jose banned plastic bags in 2012 and currently reports 69 percent fewer plastic bags in its trash screens and 71 percent fewer plastic bags in its creeks.

But in most of California, bags are still distributed free by stores, and those bags don’t respect boundaries. Millions of plastic bags from other cities still blow and flow into our shared waterways or are carried to beach destinations like San Francisco, Santa Cruz and Monterey to become marine debris.

More than 1.3 million plastic bags were picked up from California beaches on just one recent Coastal Cleanup Day. So it’s no surprise that 90 percent of floating ocean debris is plastic, which never biodegrades.

For all of us who treasure California’s creeks, bays and beaches, and the fish and wildlife who live in them, Proposition 67 is a crucial opportunity to prevent billions more plastic bags from becoming toxic, deadly litter throughout the state. Voting Yes on 67 is also our chance to show the nation and the world how to stand up to the plastic bag industry, so other states and countries follow our example and rescue the world’s oceans from the plastic trash that is choking them.

David Lewis is executive director of Save The Bay (www.saveSFbay.org). He wrote this for The Mercury News.