Hundreds, perhaps thousands, of fish are dead on the Floyd River after nitrogen spilled Monday at the Midwest Farmers Co-op in the northwestern Iowa town of Sheldon. The environmental impact is still being assessed. The D-N-R says the liquid nitrogen spilled when a transfer pipe split between a storage tank and a railroad car. The fertilizer fell outside a containment dike designed to prevent accidents and flowed into a storm drain. The river is partly dammed with hay bales as the stream is being pumped into a field. Four inches of ice on the stream are hampering efforts.