The EPA's assumption that a farm with no record of discharges would violate the law in the future was, in the judges' words--an attempt by EPA to create from whole cloth new liability provisions.
The court declared the farms only need permits if they actually discharged, which is a violation of the Clean Water Act. The likelihood that they would discharge was not enough to trigger the permitting process, which farmers find cumbersome and expensive.
The ruling is only binding for now in the Fifth Circuit, which covers Louisiana, Mississippi and Texas.
http://www.usagnet.com/story-national.php?Id=1030&yr=2011