Madrid, Spain ? Small portions of an oil slick reached the coast of northwest Spain on Saturday after a heavily loaded oil tanker ruptured several days ago in a storm.

The Bahamian-registered Prestige, with most of its 85,000 ton cargo, remained tenuously secured to tugboats about 104 miles into the Atlantic Ocean. In rough weather and unable to proceed under its own power, the Prestige has a 50-foot crack in its hull below the waterline.

“Ideally, we’d like to get it to a point of shelter. But due to the storm, that doesn’t look possible. We’ll just have to wait for the bad weather to change,” Lars Walder of the SMIT salvage company said in a telephone interview from Holland.

The tanker leaked Wednesday during a storm. The vessel is considered to be vulnerable because its hull has no outer casing to provide extra protection against leakage. Details on how the ship began to leak were unknown, officials said.

The next 20 hours will be critical, Walder said.

As winds reached 50 mph and waves topped 23 feet, SMIT’s experts ran the tugboats and intended to attempt to land a repair crew by helicopter on the Prestige, whose crew had been evacuated and captain arrested for negligence.

The oil reaching the shore apparently is from the Prestige’s leak of about 3,300 tons following an accident Wednesday night that apparently cracked the right side of the hull.

A bird covered with oil sits on the rocks in Malpica, northwestern Spain. Oil spilled from the Bahamas-flagged tanker Prestige washed ashore Saturday.

“We will do all we can to avoid a disaster,” a spokesman for the Interior Ministry in the northwestern city of A Coruna said on condition of anonymity, noting clean-up operations already were under way. Authorities set up 5 miles of floating barriers and 14 oil-sucking skimmers.

There were no immediate reports of damage to wildlife.

The environmental group World Wide Fund for Nature-Adena warned that the ship may end up over the Bank of Galicia, a rich breeding ground for coral, spongers and fish located about 124 miles offshore.

Walder said the next step was to turn the Prestige around so the damaged hull was protected from the waves, at which point it might be possible to repair the crack or transfer the oil to another ship.

Spain doesn’t want the damaged ship traveling near shore, entering a Spanish port and possibly endangering shipping, the environment or tourism.