Over 80,000 American crayfish have been netted in waterways in Krimpenerwaard near Gouda in a failed attempt to limit their number.

The crayfish – Procambarus clarkii, or red swamp crayfish – are thought to have travelled from their native United States in the ballast tanks of large freighters and are well adapted to local waterways. They are particularly common in Utrecht, Noord-Holland and Zuid-Holland.

First spotted in Dutch waters in 1985 and without any natural enemies, crayfish numbers are now thought to be running into billions. Their presence is said to be a threat to water flora and fauna and they also damage to river banks.

The crayfish caught in Krimpenerwaard were adults and had already procreated so in that sense the operation has been a failure, local water authority spokeswoman Paula Korteweg told NU.nl.

However, the project was also a first step in an investigation into what is needed to solve the problem. That, Korteweg said, can only happen if there is a national plan similar to the approach taken to control muskrats.

Korteweg said it would also help if no license were needed to catch crayfish for private consumption. They are already making their way to restaurants in great numbers.

It is up to the government to enable a concerted effort to rid Dutch waters of the harmful invader, she said.