A mudslide in Bellingham that blocked traffic on I-5 for hours was caused by a blocked culvert, according to the Washington State Department of Transportation.

The city of Bellingham says a clogged culvert is likely to blame for the landslide that shut down northbound Interstate 5 in Bellingham Sunday.

After heavy rain, a landslide blocked all northbound traffic on Interstate 5 by Iowa Street. Here are the numbers behind the cleanup effort.

The slide was caused by a blocked culvert that resulted in water buildup during a heavy period of rainfall, and doesn’t appear to indicate slope instability, representatives from the Department of Transportation (WSDOT) and City of Bellingham Public Works said.