The report to Congress was blunt: The U.S. Environmental Protection Agency had failed to regulate pollution from the nation’s livestock farms — many capable of generating more waste than some cities — because it lacked information as basic as how many farms even existed.

Four years after the Government Accountability Office raised concerns and 40 years after the Clean Water Act gave the EPA the authority to protect the nation’s waterways, the agency still doesn’t know the location of many livestock farms, let alone how much manure they generate or how the waste is handled, because most of that information is kept by various state and/or local agencies — or not collected at all.

At the same time, water-quality experts throughout the country cite livestock waste as a major contributor to water-quality problems, including in areas like the Chesapeake Bay, where manure runoff is believed responsible for up to one-fourth of phosphorus, which stimulates algae growth. If the EPA knew all the sources of that waste, it might be easier to stop it, environmentalists say.

So they were flabbergasted when the EPA recently decided against adopting a rule that would require livestock operators to provide the agency with information, opting instead to try to cobble it together from other state, local and federal sources — a decision they said puts the EPA right back where it started.