Brazilian activist and fisherman Alexandre Anderson uses one hand to steer his boat, and the other to film an oil stain spreading over Rio de Janeiro's Guanabara Bay.
He will upload the video to an app developed to expose environmental damage in the iconic bay crucial for tourism and the fishing industry, but plagued by spills of oil, chemicals and untreated wastewater.
Guanabara Bay, a natural port of about 400 square kilometers (154 square miles), battles pollution not only from visiting vessels and oil rig accidents, but also from old ships abandoned in its waters and runoff from cities.
Frustrated with what they see as a lack of official response, the bay's fishermen decided to take matters into their own hands, and with the backing of non-governmental organization 350.org, had an app developed for them.
"We used to take pictures with our cell phone or a camera," but without exact geolocation data, it was of little use, Anderson -- president of the bay's Ahomar fishermen's association -- told AFP as he filmed a steady stream of wastewater being dumped from a ship.
The app, however, "gives me the precise" data with which to file a complaint, anonymously.
The information is verified by a moderator and published on a dedicated website, after which it is reported to authorities such as the country's Ibama environmental regulator or Brazil's navy, which patrols the bay.
Every time he monitors the dark waters for just a few hours, Anderson encounters several illegal spills, he says.
Within three weeks of the app launching on July 26, 20 complaints were posted on the web, and more than 100 others are under analysis, according to administrators.
- 'Practically' no more sea bass or hake -
"The inspection agencies always claimed they don't have the tools to deal with complaints," said Paulo Barone, who belongs to another local fishermen's association.
But with this new app, he said, the authorities "can no longer deny or ignore" the complaints.
For 350.org's Brazil coordinator Luiz Afonso Rosario, artisanal fishermen have been on the "front lines" for too long.
"Oil and gas companies, in addition to polluting the waters that are a source of food, income and leisure for thousands of families, aggravate the climate crisis... by providing fossil fuels that are the main cause of global warming," he said.
Fishermen were particularly hard hit by a spill in 2000 that saw 1.3 million liters of oil dumped into the bay from a Petrobras refinery.
"That ended the fishing. You practically don't find any sea bass (or) hake anymore," said Roberto Marques Resende, who still fishes in the region.
For some, the battle is about more than even subsistence.
Anderson, who has been standing up to the petrochemical industry for years, says he has been the target of threats and attacks for years and hopes that the app will help ensure that "those responsible are really punished."
"Only then will we solve these problems," he said.