The U.S. Environmental Protection Agency says it will study whether to toughen regulation of large livestock farms that pollute waterways. The agency hasn’t revised its rules dealing with the nation’s largest hog, poultry and cattle operations since 2008. Farm manure and fertilizer runoff fouls lakes and streams. It’s a leading cause of harmful algae blooms. EPA says it reconsidered its intention to leave existing rules in place after an environmental group filed a lawsuit. The agency says it will gather information on how bad the pollution is and what new methods might bring improvements.