Over 11,000 American crayfish have been caught in the Proosdij pond in Ede in a month-long attempt to control the population.

The number of crayfish invaders far exceeded the expected catch of between 2,000 and 4,000.  Local water boards decided to take action when the water quality in the pond started to deteriorate and plant life disappeared.

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 and the association of local councils VNG have called on the agriculture ministry to take action.

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 a threat to water flora and fauna and they also damage to river banks.

The crayfish fishing expedition, set up by research bureau ATKB with the help of a local fishing club, has resulted in slightly clearer water, fisherman Peter Dorlas told local broadcaster Gelderland.

‘We are hoping the banks are bit safer as well. The crayfish are digging holes in the bank. You sit down on your fishing stool and the legs disappear into the ground or you end up in the water. Children can step into the holes and sprain their ankles. It’s downright dangerous.’

Dorlas said the pond will probably have to be divested of crayfish every year to keep the population in check.

The pond will be checked again after the summer for any remaining crayfish. The ones that were caught will be sold off to restaurants.