* Exxon says has notified government agencies
* Fisherman say can't access toxic fishing waters
* Oil spills common in Africa's top producer
LAGOS/PORT HARCOURT, Nigeria, Aug 15 (Reuters) - E xxonMobil's Nigeria unit said it was investigating an oil spill near its facility off the country's southeast coast, which local fishermen said had covered the waters where they fish with a toxic film.
Mobil Producing Nigeria, a joint venture between ExxonMobil and the state oil firm, said on Wednesday that relevant government agencies had been notified of the spill.
"Mobil Producing Nigeria ... confirms that oiling from an unknown source has been sighted along the shoreline near Ibeno, Akwa Ibom State," spokesman Nigel Cookey-Gam said.
"An emergency response team was immediately dispatched to the shoreline, and samples of the substance were collected for fingerprinting to determine its source, which remains unknown."
Sam Ayadi, a fisherman in Ibeno, said by telephone that no one had been able to go fishing since the spill was first noticed on Sunday.
"The fishermen are still off the waters due to the spill. We cannot return yet. We are waiting for Mobil to open to discussions with us about what happened," he said.
Oil spills are common in Africa's top energy producer. Stretches of the Niger Delta, a fragile wetlands environment, are coated in crude. Thousands of barrels are spilled every year, and lax enforcement means there are few penalties.
The companies say the majority of spills are from armed oil thieves hacking into or blowing up pipelines to steal crude, an activity they estimate saps nearly a fifth of Nigeria's output.
A landmark U.N. report in August last year slammed the government and multinational oil companies, particularly leading operator Royal Dutch Shell for 50 years of oil pollution that has devastated the Ogoniland region.
The government and oil majors have pledged to clean up the region and other parts of the delta, but residents say they have seen very little action.
"Because of this spill we have not been going to fish again since Sunday. So we are suffering because this is the only work we do as fishermen," Inyang Ekong said.
"This is what we go through each time there is a spill, and that is why the prices of fish are going higher everyday."
Several communities have taken Shell to court over a failure to clean up spills, although the oil major says insecurity and rampant oil theft are hampering clean up efforts.