Aa

The Aa (French pronunciation: [a]; Picard: Abbe) is a river in northern France that is 93 km (58 miles) long. Originating near the village of Bourthes and emptying into the North Sea near Gravelines, the Aa is located near the north-eastern limit of the English Channel. The Aa has been canalized for most of its length and forms much of the border between the regions of Pas-de-Calais and Nord.

Source: Wikipedia https://en.wikipedia.org/wiki/Aa_(France)