(Harrisburg) -- Thousands are being ordered to evacuate or encouraged to leave their homes as the Susquehanna River rises. Forecasters fear the river may crest at levels not seen in decades. Ben Pratt is with the Susquehanna River Basin Commission. He says after yesterday's flash flooding and small stream and creek flooding, flooding along the river is what's next. "As the rivers are approaching and exceeding flood stage now, we're not expecting crests in the lower part of the Susquehanna, that would be Marietta and Harrisburg, until Saturday sometime," he says. Freight train traffic along the Susquehanna has also been impacted by the rising waters. Rudy Husband of Norfolk Southern in Pennsylvania says there's nothing the railway can do at this point. "Right now, we have some flooding between Reading and Harrisburg, which caused us to shut that main line down," he says. "We have a line that runs up along the east bank of the Susquehanna River to Sunbury, and we've shut that down." Harrisburg serves as a main junction point for Norfolk Southern, so Husband says the flooding is having a significant impact on its services.