That's because the Corps of Engineers has drained all the water from the 35-foot tall lock to inspect and fix all its components.
Matt Thurman, Chief of Maintenance for the Rock Island District Mississippi River Project Office, says inspection can't be done at any other time. One job is to replace long, metal pipes he calls "bubblers." Workers use them to clear debris from the gates while they're moving, preventing damage.
His employees are also replacing the steel and concrete gate hinges at both ends of the 600-foot lock. They're also doing a lot of concrete and steel work on the walls and floor of the lock chamber.
Lock 15 hasn't been "dewatered" for around 25 years. Two years ago, the corps installed new gates. Thurman says the project will be completed in March, in time for navigation to resume. Lock 14 upstream at LeClaire was drained, inspected, and repaired last year.
This month, the corps announced it'll receive $1.2 billion in infrastructure and disaster relief funds. The Rock Island District will be in charge of several projects including the extension of Lock and Dam 25 from 600 to 1,200 feet.