The size of vessels that can traverse the seaway is limited by the size of locks. Locks on the St. Lawrence and on the Welland Canal are long, wide, and deep. The maximum allowed vessel size is slightly smaller: long, wide, and deep. Many vessels designed for use on the Great Lakes following the opening of the seaway were built to the maximum size permissible by the locks, known informally as Seawaymax or Seaway-Max. Large vessels of the lake freighter fleet are built on the lakes and cannot travel downstream beyond the Welland Canal. On the remaining Great Lakes, these ships are constrained only by the largest lock on the Great Lakes Waterway, the Poe Lock at the Soo Locks (at Sault Ste. Marie), which is long, wide and deep.