Resident Sarosha Stockton says he found dead fish and jet fuel in the Slocan River on Saturday, some 24 hours after the spill.
In a video he uploaded to YouTube, he points to a "rainbow of fuel" in a shallow pool in the water by the shore, as well as eight to 10 dead juvenile fish along a small stretch of the river.
It is unclear if the jet fuel killed the fish, but Stockton says the authorities need to do more to protect the river.
"It's a tragedy," said Stockton, noting that there were no booms in the area where Lemon Creek flows into the Slocan River, only further downstream.
Stockton warned people to stay away from the river, saying the air was hard to breathe on Saturday because of a strong jet fuel smell.
He also pointed out areas where the water appeared milky from potential jet fuel contamination.
A tanker truck carrying jet fuel for helicopters fighting forest fires crashed into Lemon Creek on Friday. Almost all the fuel in the tanker, about 35,000 litres, spilled into the creek.
Residents in the area who were advised to leave their homes Friday night were told it was safe to return on Saturday.
The evacuation zone affected about 1,500 people at one point.
A hazardous materials team from Vancouver has been sent to the area to work with local fire departments and other agencies to contain the spill in local waterways.
Officials said earlier that there were no reports of fish or wildlife being affected. They say that unlike crude oil, jet fuel in a waterway dissipates much more quickly.