Residents are preparing for a potential overflow as runoff courses into neighboring Nebraska towns.
"The exact crest stages are still uncertain as the waters are just moving into Nebraska," the National Weather Service said.
"It is possible that upcoming forecasts could change so those along the river should stay tuned for updated information."
In 2010, the Platte River felt the burden of severe ice jams caused by freezing temperatures and low water levels. Now, the river is likely to catch the aftermath of Colorado's flooding.
Sandbagging and emergency levees are being put up at the Nebraska-Colorado border to protect towns at risk, including Roscoe, Paxton, North Platte and Brady.
Record flooding is anticipated, with some parts of Nebraska seeing their greatest water levels in 80 years.
Flooding started September 11 following heavy rains in Colorado and affected at least 17 counties, and waters have destroyed 1,500 homes and damaged 4,500 more.
About 300 people remain unaccounted, but police suspect that those on the unaccounted list are likely alive and well.