Dozens of illegally dumped goldfish have been rescued from a stream in Arnhem in the second operation of its kind in six months.

A total of 186 fish were removed from the Sint-Jansbeek at the weekend and transferred to a secluded pond. The water authority for Rijn and IJssel is cleaning up the waterway so that it can introduce pike in the near future.

A spokesman for the authority said all the fish had been illegally put in the stream by humans, possibly in response to a similar incident earlier in the year. In April, 11 fish were dumped in the Sint-Jansbeek, only one of which was recovered, but the specimens found at the weekend were too big to have been the result of breeding.

Goldfish are an invasive species that upset the balance of the ecosystem in Dutch waterways, the water board told NOS. ‘They can survive here, but they drive out other fish that are better suited to this kind of water system,’ said the spokesman.

He added that the pike were better matched to the environment in the stream. The predatory species is big enough to feed on the goldfish, but the water board wanted to remove them first. However, as the spokesman acknowledged: ‘There is a big chance that one or two fish have slipped under the net.’