A nearly mile-long slick of an unknown pollutant was spotted moving down the Danube river in Ukraine toward the Black Sea, Ukrainian officials said Tuesday, according to AP.

The nearly one mile-long and 16-foot-wide slick, which was detected Monday in the Ukrainian segment of the Danube river, is believed to have come from neighboring Romania, said Sergei Zablotsky, spokesman for the regional branch of Ukraine`s Emergency Situations Ministry.

Zabolotsky alleged the slick could be the result of a Romanian plant dumping technological waste into the river. Environmental officials were taking samples of the substance to determine its nature and whether it represented any danger, he said.

Officials in Romania could not immediately be reached for comment.