Greenpeace has called on Spain's government to dedicate more resources to cleaning up an oil spill rising up from a sunken fishing trawler off the Canary Islands after spotting a five-kilometer (3-mile) slick.

The group said one of its planes had detected "thick oil" covering the ocean just above where the Russian fishing boat Oleg Naydenov sank on April 14, about 24 kilometers (15 miles) south of the tourist hot-spot of Gran Canaria.

Development Ministry spokesman Julio Gomez acknowledged Sunday that slicks were being monitored; a day after the government activated an alert, saying oil could damage the islands' vulnerable coasts.

The trawler, which carried 1,400 metric tons of viscous fuel oil, sank after catching fire in an island port and being towed out to sea as a precaution.