An oil spill in 2014 in the Kukama Indigenous community of Cuninico, on the Marañón River, as well as more than a dozen others since then, came from the Northern Peruvian Pipeline, which was built in the 1970s to transport crude from the country’s then-new Amazonian oil fields across the Andes Mountains to the Pacific coast. The 687-mile pipeline was an engineering marvel at the time, but by 2014 it had aged and corroded. A government oversight agency determined that the pipeline had not been properly inspected and maintained.

The two oil fields — Block 192, which was originally called 1AB, and Block 8 — are also crisscrossed by aging pipelines and riddled with pollution from spills that were never properly cleaned up. The fields have their roots in an oil boom that struck Amazonian Peru in the 1970s, engulfing scores of tiny communities that would suffer the consequences over the next half-century.

At the time, the Peruvian government was anxious to compete with neighboring Ecuador, where the US-based oil company Texaco had begun operating in 1967, and establish the national boundary more firmly in the wake of a vicious border war. Around the same time, an energy crisis triggered by production cutbacks by the Organization of Petroleum Exporting Countries had prompted US oil companies to look for other sources.

Petroperú struck oil in the Corrientes River basin in 1971, and U.S.-based Occidental Petroleum quickly followed suit nearby. New legislation gave foreign companies tax breaks in exchange for turning over to the Peruvian state half the oil they produced, and nearly a dozen obtained concessions in the next two years.

Most of the oil was heavy crude, though, making it expensive to extract. The boom petered out, and most of the foreign companies were gone by the mid-1970s. Occidental Petroleum took over Block 1AB and Petroperú operated in Block 8, which included a fragile wetland area that is now part of the Pacaya Samiria National Reserve.

In the early years, when production was highest, nearly two-thirds of Peru’s oil came from the Amazonian fields in Loreto. Over time, however, that has declined, and in recent years the pipeline, built to transport around 100,000 barrels a day, has operated at barely one-quarter of its capacity.

By the 1980s, even the Peruvian government recognized that Block 1AB was one of the most polluted places in the country, its ecosystems damaged or destroyed by inadequately protected waste dumps, spills that were never cleaned up, and produced water — the hot water, high in salt and metals, that is pumped out of wells with the oil — that was simply dumped into rivers and streams.

Because the oil concessions have changed hands, responsibility for cleanup has become a matter of finger pointing, as it is difficult to prove which company was operating the lot when individual cases of pollution occurred.

Block 1AB/192 was operated by Occidental from 1971 to 2000, the Argentinian company Pluspetrol from 2000 to 2015, and Canada-based Pacific Stratum, later Frontera Energy, from 2015 to 2021. The block is currently idle, but state-owned Petroperú has said it plans to operate it with a foreign partner.

Petroperú operated Block 8 until 1996, when Pluspetrol took it over. Pluspetrol, which is now based in Amsterdam, declared itself in liquidation in December, throwing the future of the block into doubt. In its announcement, the company blamed Peru’s environmental oversight agency for holding it responsible for pollution that occurred while other companies were operating the block.

Achuar communities on the Corrientes River sued Occidental Petroleum in US courts in 2007 for environmental damage, reaching an out-of-court settlement for an unspecified sum in 2015. Other communities have sued in Peru over environmental damage and health problems, but the pollution persists.