A nearly half-mile segment of coastline in Huntington Beach and Newport Beach at the Talbert Channel reopened to surfers and swimmers Monday morning after a large sewage spill caused a weekend cessation of water activity. Orange County Health Care Agency officials on Saturday called for the temporary closure along beaches 1,000 feet to the north and south of the channel, near the mouth of the Santa Ana River, to protect visitors from potential exposure to bacteria. The spill stemmed from a blockage discovered Friday evening in a sewer line on Costa Mesa’s Mesa Verde Drive East, near Golf Course Drive, according to Scott Carroll, general manager of Costa Mesa Sanitary District.