Worsening pollution in the Olympic Peninsula's Dungeness Bay is prompting state health officials to order the first-ever closure of some commercial shellfish tideslands there. The closure of a 300-acre section of the bay will begin in late April. Among those affected will be members of the trivbe, who raise oysters on tidelands they both own and lease from Clallam County. The tribe has been preparing for a closure, moving oysters from the affected beds to clean water elsewhere in the bay, said Mark Madsen, the tribe's director of economic development. But future revenue is at stake if the bay and river aren't cleaned up, he said. "Long term, this is a big hit,'' Madsen said. He estimated closure would cost the 450-member tribe $50,000. The move is a result of high levels of fecal coliform bacteria, mostly from human and animal waste leaking from home septic systems and barnyards in the Dungeness River watershed. State shellfish specialist Don Melvin said the rising bacteria count has been a concern for years. Harvesting of crab, shrimp and fish will not be affected by the ruling. Dungeness Bay is just the latest area where harvesting has been prohibited.