And those lining the route to cheer on the runners should bring an umbrella as forecasters predict it will be a wet race day.
The marathon is taking place in Derry on Sunday, June 3, between 7 am and 3 pm.
The main affected routes are: Victoria Road, Limavady Road, Foyle Road, Strand Road & the City Centre.
“Police advise that road users at these locations proceed with due care, comply with the traffic management road signage and exercise patience during this event,” said a PSNI Foyle spokesperson.
“We thank you for your attention with this matter.”