Once the needles have been placed closely together, they form a wall which can hold back the waterway on both sides of the lock. When it is sealed, water is pumped out of the lock chamber. Once the area is relatively dry, equipment, materials and crews can be lowered into the chamber to conduct inspections and begin repairs. (USACE Jacksonville District photo from a 2012 maintenance repair project at the St. Lucie Lock in 2012)