The infrastructure ministry has again warned people seeking to escape the heat not to swim in the country’s bigger rivers.

On Thursday, a 13-year-old boy became the third person in a week to drown while swimming in the river Waal, a tributary to the Rhine which connects Rotterdam to Germany.

The boy, said by local broadcaster Omroep Nederland to be a Syrian national, disappeared while swimming in the river with friends.

‘People are not aware of the dangers’, spokesman Diederik Fleuren told broadcaster NOS. ‘And they over-estimate their own swimming skills. Rivers have strong currents, wide differences in temperature and shipping. All in all, we would say don’t do it.’

Swimming is currently only banned in river shipping lanes.

Fleuren said the department does not keep a record of how many people drown in rivers but said it is certainly in the dozens. ‘Their number often includes foreigners who cannot swim well,’ Fleuren said.