Vast stretches of the Limmat River were transformed into the lurid fluorescent colour as it stretched through the old town region of the Swiss city.
Extinction Rebellion activists wearing t-shirts with the group’s logo shared pictures of themselves on social media floating face up and motionless along the river.
The Zurich wing of the protest group took responsibility for the action on Facebook. It said it to “draw attention to the impending collapse of the ecosystem, and to the toxic system in which we live”
They added the dye was made from uranine and carried the same levels of toxicity as table salt.
The action is part of a “September tour” of protests due to spread across Switzerland, with action impacting Geneva, Fribourg and Lausanne in the coming days.
Police in Zurich are reportedly analysing the substance after receiving multiple calls from the public.
The group, which was founded in the UK and staged its first action in October last year, takes inspiration from protests including Ghandi’s Satyagraha and the US civil rights movement.
It pushes for radical change and urges governments to call a state of “climate and ecological emergency”.
Since its inception Extinction Rebellion has caused peaceful disruption in cities across the world, bringing major thoroughfares in central London to a standstill as protesters occupied roads and glued themselves to buildings and trains.
Further action is expected in October, when the group has called for an “international rebellion”, which is expected to see further blockades.
More about: Zurich