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U.S. endurance swimmer Diana Nyad has begun her second attempt in as many months to traverse 103 miles of sea between Cuba and Florida.

The 62-year-old Los Angeles woman is hoping to break her own world record for open-water swimming without a shark cage.

A previous attempt last month fell short after asthma forced her to give up about halfway. Nyad insists she's ready to brave the choppy seas, schools of jellyfish and limits of exhaustion to accomplish her lifelong dream.

She waved goodbye to well-wishers at Havana's Hemingway Marina on Friday evening.

Assistants smeared grease on her shoulders to prevent chafing during the planned 60-hour journey. She jumped feet first into the still waters, then steadily began stroking her way out to sea.