Finland's two oil spill response vessels are in still in dock at Rauma Harbour on the west coast awaiting winds to decrease.
The Institute estimates the slick will reach Finnish shores by the end of the week at the earliest. Westerly winds are blowing it in the direction of Pori on the west coast.
About one quarter of the oil split from the Arizona Chemicals plant in Söderhamn has been cleared away in Swedish waters.
Inspector Uljas Hietapakka of Finland’s Environmental Institute told YLE the slick could have a large impact on the coast. He noted pine oil, a derivative from wood processing, was a natural substance but dangerous to the environment. He added that if the oil dissolved into a thin film, it would very difficult to clean up.