It’s not an exaggeration to say that the Río Bogotá serves as a sort of sewer for more than 8 million residents of Colombia’s capital and hundreds of thousands more along its basin.

Millions of gallons of industrial chemicals, farm run-off, household detergents and human waste drain unfiltered into the Bogotá River from its source in the high Andes to its end at the Río Magdalena.

“In 2008, we had to bring oxygen masks and wear special clothing because the river was toxic”

It’s widely considered one of the world’s most polluted waterways.

“Since 1952, the Bogotá aqueduct system has been contaminating the Río Bogotá, and we are still debating what to do about it,” said Fernando Vásquez, director of Fundación Al Verde Vivo, an environmentally focused non-governmental organization.

“In the meantime, we’re throwing the waste from millions of people into its waters.”

Almost no animal can survive for long in the anoxic waters of the Río Bogotá as it approaches and flows through the capital city — what’s known as a “dead river.”

But Colombians haven’t given up on the Bogotá River yet. Thursday marks the Día del Río Bogotá (Bogotá River Day), a day-long effort to raise awareness of the state of the waterway and efforts to bring it back to life.

And there are some indicators of hope.

“What we observed, having navigated the river on two occasions, is that efforts to clean it have had an effect,” said Juan Andrés Moreno, of Cantoalagua, a cultural and environmental campaign supporting protections for water resources.

“In 2008, we had to bring oxygen masks and wear special clothing because the river was toxic. The water quality remains dangerous, but last year we didn’t need masks or special clothes,” he said.

In recent years, the Ministry of the Environment and Ministry of Health have worked together to establish maximum acceptable levels of phosphorous and other potentially dangerous chemicals in the river’s waters.

Laws have also been passed to regulate what substances can legally be emptied into the basin. And education campaigns hope to raise awareness of the problem.

“Environmental education is a key component in the recuperation of the Bogotá River,” said a Ministry of the Environment representative. “That’s why we have worked to draw attention to the protection of wildlife and plants, the ecosystems and overall functioning of the waterway.”

The most critical segments of the river are just before and just after it passes through the capital, according to the Regional Observatory on Environmental and Sustainable Development of the Bogotá River (ORARBO).

Water quality indicators at almost all points along the river’s course have improved since 2014, based on ORARBO data.

It was in that year that a Council of State judgment ordered that basic sanitation and water quality improvements be the top priorities for recuperating the Bogotá River. The ruling was an attempt to coordinate more than 30 years of failed or delayed efforts to clean up the basin.

“Fortunately there has been a judgment, which absurdly took 10 years to ratify,” explained Vásquez. “So in total it took 20 years to recognize what should have been obvious — that the Colombian state is responsible for the river.”

Essentially, the plan is to shore up existing water treatment facilities and build new ones, widen and restore the riverbed, develop a comprehensive policy on solid waste, and reforest and restore the ecosystem.

It’s a multi-level project, given that the river runs through dozens of municipalities, including the national capital. Well over 8 million people live in the area that drains into its bed.

But the same factors that have prevented significant progress over the past three decades seem likely to stymie it in the future. Budget issues, inter-governmental disputes and regulatory challenges, among other hurdles, pose a threat to recovering the Río Bogotá.

According to Vásquez, too much effort has been focused on protecting populations settled too close to the riverbanks rather than addressing more pressing problems of pollution.

But, aside from a badly needed water treatment plant, efforts to restore the river are underway.

In recent years, public and private groups have planted more than 100,000 new trees in order to help clean the air and water near the river, for example, according to the Ministry of the Environment.

The Río Bogotá begins in the Guacheneque Páramo, or moorland, some 3,400 meters (11,150 feet) above sea level. From there, it winds its way down mountains and mesas for 380 kilometers (236 miles) before reaching the Magdalena River near the town of Girardot at just 280 meters (920 feet) above sea level.

Given the dramatic change in altitude, much of the river is not navigable, but it serves as a drainage basin and water source for hundreds of thousands of hectares of land and millions of people in Colombia’s central Andes.