Accumulation of ships at a port to the extent that ships arriving to load or discharge are obliged to wait for a long time for a vacant berth. There are various reasons for congestion like strikes, severe weather, or a seasonally high volume of cargo arrival. When liner ships suffer prolonged delays - as a result of congestion, their operators impose vary often, on shippers, a "congestion surcharge".In order to avoid loss to owners due to non-availability of the berth or waiting at the anchorage, C/Ps specify that the notice of readiness can be tendered by the master ?whether in berth or not (wibon), whether in free pratique or not (wifpon), and whether customs cleared or not (wccon)