Martha Alfred used to harvest 20 bags of cassava each year before an oil spill forced her to abandon her field and hawk roasted fish to survive.

Her smallholding at Ikarama-Okordia, a community in southern Nigeria's Bayelsa state, became unfit for growing crops after crude from a nearby Shell facility spewed into the environment last August, she says.

Today, the 33-year-old mother of two looks angry and helpless, her woes compounded by downpours during the last rainy season that flooded her land.

"The soil has become infertile because of the spills," Alfred told AFP.

"Each time I remember the spills and now the floods, my heart bleeds," she said.

"People from Shell came and promised to do something for me. Up until now I have not heard from them."

Ikarama-Okordia, a collection of villages, is one of the most polluted sites in the oil and gas-rich Niger Delta.

A major pipeline that passes through the fishing and farming community of 50,000 people has been the subject of spills and militant attacks for over 20 years.

Shell said it recorded a total of 21 spills in the area between 2009 and 2018.

Overall, rights groups say that millions of barrels of crude have leaked out across the Niger Delta region over the years.

The oil companies blame most of the leaks on sabotage from local residents and criminal gangs stealing the crude.

But under Nigerian laws, the firms are obliged to clean up all spills whatever their cause.

Villagers argue some spills are due to operational factors.

"It's not completely true all the incidents are caused by sabotage. Some of them are due to equipment failures," Ikarama community leader Morris Lamiengha told AFP.

Asked about the allegations from the residents of Ikarama-Okordia, Shell insisted it meets its obligations on all clean-ups and helps affected communities whatever the reasons for the leakages.

"Shell has always and will always live up to its responsibility," spokesman Bamidele Odugbesan told AFP.

"The problem we face is re-pollution. After we clean a site, the vandals will go back and damage the facility to steal the oil without considering the negative impact on the environment."

'Destroyed the ecosystem'

A vicious cycle is repeated across the entire region: environmental degradation, pollution, neglect, under-development, anger, frustration and pain.

In oil-rich Ogoniland, it took a 2011 United Nations Environment Progamme (UNEP) report before the government launched a clean-up of the spills in the area that looks set to last some 30 years.

In Oloibiri, where crude was first discovered in Nigeria in 1956, the locals live in abject poverty. No jobs, roads, hospitals and schools.

The Oloibiri oil well no longer produces and is overgrown with weeds, while the residents drink and wash in stream water.

A government promise in 2001 to erect an oil museum in Oloibiri as a monument to the first oil well in Nigeria has yet to be fulfilled.

Locals and environmental campaigners say oil majors like Shell, Exxon Mobil, Eni, Total and Chevron, are not doing enough for host communities despite many decades of oil exploration in the region.

Nigeria, Africa's largest producer, produces an average of two million barrels of crude per day, which accounts for 90 percent of foreign exchange earnings.

"The oil firms have destroyed the region's ecosystem through their operations," said Michael Karikpo of Environmental Rights Action lobby group.

He said the people's mainstay of farming and fishing has been ruined without providing an alternatives, forcing local residents to engage in criminality for survival.

"That's why incidents of bunkering, oil thefts, pipeline vandalisation and illegal refineries will continue in the Niger Delta," he said.

He said only very few Nigerians were benefiting from oil money, while tens of millions eke out a living on less than two dollars per day.

For him, the only way to avoid spills is do away with oil production entirely.

"We should stop oil production in Nigeria because of its negative impact on the people and the environment and focus more on renewable energy," he added.

'Sitting on gunpowder'

Anyakwee Nsirimovu of Niger Delta Civil Society Coalition said the nation is "sitting on a keg of gunpowder if nothing is done to address the grievances of the oil-producing communities".

He said rather than being a benefit, "oil has been a curse for the people", adding that there was little or nothing to show for the billions of dollars made from the sector.

"Our situation is like someone who lives at the bank of a river but washes his hand with spittle," he said.

He recalled the unrest in the region in the early 2000s by militants seeking a fair share of the nation's oil wealth for the local people.

Months of militant attacks on pipelines and oil infrastructure slashed Nigeria's output to less than a third at the time, hurting government revenues.

It took a 2009 government amnesty for the oil rebels before they laid down their arms and halted the attacks.