Thousands of gallons of diesel were released into the Tennessee River after a tugboat sank in northwest Alabama, prompting calls for swimmers to get out of the water after the fuel began washing up on nearby shores, authorities said Sunday.

The tugboat sank near O' Neil Bridge and began to release roughly 3,000 to 5,000 gallons of diesel into the water, the Florence Alabama Police Department said in a news release.

"Diesel fuel has began to wash up the beaches of McFarland Park," the department added.

People who were swimming at McFarland Park in Florence were asked to get out of the water, according to the release. The park is a popular destination for families that features a beach area, fishing piers, playgrounds and campsites, according to the city's website.

"Please stay out of the water and off the beaches until further notice," the release read.

A photo released by Florence police showed an iridescent sheen floating on the water near the bridge.

No one was aboard the tugboat when it sank, and it's unclear what caused it to go down, the City of Florence and Lauderdale County Emergency Management Agency Director George Grabryan told CNN.

CNN has reached out to the police and Environmental Protection Agency for more information.

Florence is approximately 73 miles west of Huntsville, Alabama.