Congressman Josh Harder Thursday stood near ground zero of where the fluctuating snowpack in the Sierra can cause serious problems when it is too little and when it is too much. Harder was at the San Joaquin National Wildlife Refuge that extends to the Stanislaus River just 10 miles south of Manteca. He was there to get an update on efforts to eradicate large invasive swap rodents known as nutrias that can seriously damage vegetation and levees.