German scientists still have no explanation for what's causing the combustion, an official said on Wednesday.
Both the pond's water and body parts of the toads have been tested, but scientists have been unable to find a bacteria or virus that would cause the toads to swell up and pop, Janne Kloepper, of the Hamburg-based Institute for Hygiene and the Environment said.
"It's absolutely strange."
"We have a really unique story here in Hamburg. This phenomenon really doesn't seem to have appeared anywhere before," she said.
The toads at a pond in the upscale neighbourhood of Altona have been blowing up since the beginning of April, filling up like balloons until their stomachs suddenly burst.
"We have a really
unique story here
in Hamburg. This phenomenon really doesn't seem to
Institute for Hygiene and Environment
"It looks like a scene from a science-fiction movie," Werner Schmolnik, the head of a local environment group, told the Hamburger Abendblatt daily.
"The bloated animals suffer for several minutes before they finally die."
Biologists have come up with several theories, but Janne Kloepper said that most had been ruled out.
The pond's water quality is not better or worse than other bodies of water in Hamburg.
The toads did not appear to have a disease, and a laboratory in Berlin has ruled out the possibility that it is a fungus that made its way from South America, Klopper said.
She said tests would continue. In the meantime, city residents have been warned to stay away from the pond.