Parts of the river in Colorado were under a flood warning in late May because temperatures warmer than the seasonal average caused snowpack to melt more quickly than normal.
Tank operator Noble Energy said it discovered a spill of about 178 barrels last week. The company said Friday the tank was damaged by high waters. The company pulled oil from a second tank as a precaution, though no drinking water was contaminated by the spill.
The Colorado Oil and Gas Conservation Commission said it was notified of the spill Friday. It's working with the Environmental Protection Agency in its response.
Noble Energy in December said the bulk of the company's spending in 2014 would target the Denver-Julesburg basin in Colorado.
The Colorado Oil and Gas Conservation Commission confirmed at least 600 barrels of oil were spilled from operations in the state after more than a foot of rain fell on parts of Colorado last autumn.
Environmental advocacy groups sounded the alarm because of the intensity of oil and gas operations in a state the U.S. Energy Department said has "enormous" deposits of oil and natural gas locked in shale deposits.