Published: Jun 20, 2010 8:28 PM EDT
Updated: Jun 20, 2010 5:28 PM EDT

MIAMI (AP) - Miami-area swimmers are being warned to stay out of Biscayne Bay after an estimated 20 million gallons of raw sewage spilled from a burst pipe.
      
The Miami-Dade Water and Sewer Department says sewage flowed from the burst pipe for about 12 hours, until it was capped Saturday morning. It's not clear what caused the rupture.
      
Health officials issued a public advisory asking residents to avoid swimming and recreational activities in the bay areas from the Julia Tuttle Causeway to the Oleta River Park.

Water quality tests are underway.