More than two million gallons of water have been drained from the Worcester & Birmingham canal so that maintenance work can be carried out.
The restoration work is being carried out on the Tardebigge lock flight - the largest in the country.
The 530m (580 yard) long Tardebigge tunnel has also been drained and refurbished.
Five out of the 30 locks in the flight are being given new gates.
The Act of Parliament to allow the building of the Worcester & Birmingham canal was passed in 1791, though the canal wasn't opened until 1815.
The canal is 47km (29 miles) long, and has five tunnels and 58 locks.
It cost £610,000 to build, the equivalent of more than £42m today.
There are 58 locks on along the canal.
The lock flight at Tardebigge raises the Worcester & Birmingham Canal by 220 feet, and is Grade II listed.
South Wales & Severn Waterway Manager Nick Worthington said this stretch of waterway contains a fascinating snapshot of waterway history:
"Whilst working in the area we have drained the Tardebigge tunnel to carry out an inspection which hasn't been done since 1978.
"It was once believed to be haunted, containing a secret brick archway below water level leading into a cavern."
The five lock gates are being replaced with new ones built by
from sustainably-sourced oak.
They are also restoring the brick work at the bottom of the lock chambers using lime mortar instead of cement, to preserve the existing structure.