In her provocative 2013 documentary Salmon Confidential, filmmaker and activist Twyla Roscovich showed how salmon farms in British Columbia were contaminating wild fish stocks. Using gorgeous footage and compelling storytelling, the film contended that Norwegian fish-farm companies had brought over dangerous viruses from Europe and that the government had covered up the problem. The message drew howls of protest from the fish-farming industry.

Her 2003 documentary RainWolves centred on footage of wolves in the Great Bear Rainforest on B.C.'s Pacific Coast. Scientists knew wolves in the region ate salmon, but they believed the animals were scavengers. Ms. Roscovich helped uncover the truth: For weeks she perched in trees to capture images of the wolves in the water, collecting proof that the wolves were catching their own fish.

Ms. Roscovich, who had little formal training, taught herself how to make documentary films and did her own research on equipment and editing techniques.

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"She worked Google like hell to learn the ins and outs," Glen Roscovich, her father, once told his stepdaughter, Leni Goggins.

"She captivated with her remarkable storytelling ability," says Alexandra Morton, the biologist featured in Salmon Confidential, who notes Ms. Roscovich had a "beautiful, gentle voice" as well. She helped other filmmakers on that front and narrated Our Living Legacy, a 2009 documentary about protecting old-growth forests by Jeremy Williams, a B.C.-based filmmaker.

While Ms. Roscovich had no advanced scientific education, she dug deep into biology research and presented it to the public. In a 2013 article she wrote for The Georgia Straight, Ms. Roscovich explains what the piscine reovirus is and how it causes heart and skeletal muscle inflammation (HSMI), a disease that makes farmed fish become sluggish for a few weeks before they recover. "It is alarming, however, to think what HSMI means for wild salmon, which do not have the luxury of resting for weeks while they recover," she wrote.

Ms. Roscovich was a skilled diver who was fearless around the water, and fearless in general. While Ms. Roscovich was filming the wolves, she came down with a serious fever, Ms. Morton recalls, which caused her to be laid up in her tent for several days – alone. When her head finally cleared, she went out and spotted wolf tracks all around the tent. "It didn't scare her," Ms. Morton says.

The first time Ms. Roscovich's father took her diving as a teen, he was worried that the current was too dangerous that day. Mr. Roscovich was panicking when his daughter was underwater and he could not see her. She soon surfaced with a huge grin on her face.

Ms. Roscovich, who lived in Sointula on Malcolm Island, went missing on Sept. 7 near Campbell River on her way to an out-of-town medical appointment. Her body was found on Sept. 15. Her family has not made public the cause of her death but indicated that there was no foul play involved. She was 38.

Twyla Jean Roscovich was born in Whitehorse on Feb. 8, 1979, to Mr. Roscovich and Lynn Zaharuk. The family, which included her younger brother, Adam, moved to Nanaimo in 1984, where Mr. Roscovich studied aquaculture. They soon settled in Campbell River and he worked on a salmon farm.

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Her parents divorced when she was in her teens and Mr. Roscovich married Deb Lesuk.

"[Ms. Roscovich] had an amazing ability to tell a story from a very early age," her father recalls. Her parents thought filmmaking might be a good outlet and signed her up for a week-long workshop at the Gulf Islands Film and Television School on Galiano Island.

"From that moment, it was what she was going to do," recalls Ms. Goggins, her stepsister. Ms. Roscovich became suddenly focused and used books and online resources to teach herself about film.

When Mr. Roscovich wrote a piece of music called Song of the Seafarm, his daughter shot a video for it that won the Best Music Video Award at the 1996 Canadian International Amateur Film Festival. She was just 17.

Soon after, she became critical of salmon farming and environmental issues became the focus of her filmmaking.

"Twyla got her environmental interest in incubation," says Mr. Roscovich. His own mother, Ruth Roscovich, is a long-time activist.

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Soon after graduating from high school, Ms. Roscovich was invited to OrcaLab, a whale-research station at Hanson Island, by one of the film school's teachers. The BBC's Natural History Unit wanted footage and Ms. Roscovich's name was put forward to do the work.

The Britain-based funders thought they were getting the experienced instructor to do the work. When they learned that the young and uncredentialled Ms. Roscovich was doing it, they nearly fired her but finally kept her on because her work was of such high quality.

From there, Ms. Roscovich launched a freelance career. She took contract jobs with organizations such as the Discovery Channel and A&E. She also shot her own films, often raising the funding herself.

By the time she shot 2003's RainWolves, her style had taken shape. She followed noted wolf researcher Dr. Chris Darimont of the University of Victoria and his research colleague Chester Starr, a Heiltsuk Nation hunter. She combined environmental warnings in her film – the wolves' habitat was being threatened by logging – with hard science and an awareness of First Nation land rights.

In 2011, she created the video Risking It All – Oil on our Coast, about the Enbridge pipeline. It was produced in co-operation with the Gitga'at Nation. Her 2013 short film, BC for Sale, which she released in advance of the 2013 provincial election, criticized the reigning Liberal Party's relationship with big business and its environmental track record.

The feature-length Salmon Confidential was made in co-operation with Ms. Morton, whom she'd met at the OrcaLab. For the film, Ms. Roscovich did underwater shots that required diving under salmon farms. It also entailed her digging both into the science and into the proceedings of the Cohen Commission, which looked into the decline of salmon in the Fraser River.

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"She really delved into the facts behind something," Ms. Morton recalls.

Critics argued that the film was biased against fish farming, including only the scientific evidence that condemned the practice.

When The Globe and Mail asked her if the film was one-sided, she said, "I suppose so. But it is from my perspective. … We did try to get interviews with the other side. They often don't want to talk, probably because of the work I have done in the past – very wild-salmon oriented.

"This whole issue seems to be split into wild salmon versus salmon-farming industries. I am definitely on the side of the wild salmon."

Last year, Ms. Roscovich released the 37-minute film Keepers of the Coast, which explores the work of four First Nations groups and their stewardship of the central coast of B.C. Ms. Roscovich featured this film and several others on her website CoastCast.ca, where she planned to feature more local environmental efforts.

Recent months had been a challenge for Ms. Roscovich. She had health issues, was struggling to raise funding for her films and had spent the spring tree planting to make ends meet. She recently split with Paul Ross, the father of her four-year-old daughter.

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"She was shockingly beautiful and tall," says Ms. Morton of her friend. Ms. Goggins says her long legs and size-nine feet made her a powerful swimmer, but she was somewhat awkward on land.

Ms. Roscovich gave generously and put most of her money into her films, while keeping little for herself.

While pregnant with her daughter, she didn't bother getting any maternity clothes until her friend Ms. Morton forced the issue. She dropped her friend off at a store and left her there until she bought something.

Friends and family recall Ms. Roscovich as a gregarious, charismatic and loving person who cared deeply about environmental issues. Says Ms. Morton: "She never wanted to hurt or embarrass anyone, she just wanted things to change."

Ms. Roscovich leaves her parents, Lynn Zaharuk and Glen Roscovich; brother, Adam; daughter, Ruby Lynn Ross; stepsister, Leni Goggins; and stepbrothers, Nygil and Christopher Goggins.