Flip-flops are the most popular footwear in the world — but where do they go when you're done with them?

Even though 3 billion flip-flops are produced worldwide, they aren't biodegradable, meaning they end up in landfills and pollute the ocean. Enter the world's first algae-based flip-flops. They're 100 percent biodegradable and are as durable as other shoes. Plus, they're cheap — the projected price is only $3.

The key is algae oil, which is converted into a type of polyurethane that can be broken down by microorganisms.

You can't buy them yet, but UC San Diego researchers say they'll be in stores by next year. That way, your next beach visit won't (hopefully) end up harming the environment.