Skipsea Castle was a motte and bailey design, with the two parts of the fortification divided by Skipsea Mere. The mere surrounded the motte; the south-east corner of the mere was cut off by two causeways to the south and east of the motte. Eels were recorded being caught in the lake during the 13th century, and the south-eastern corner may have formed a fresh-water fishery. A curved channel, approximately in size and ultimately leading to the North Sea, flowed around down the south-west side of the motte, giving boats access to wharves along the inside of the bailey, and concluded in a possible boat yard at the eastern end of the channel. There may have been an additional inland harbour just to the west of the bailey, but archaeologists are divided on this issue.