According to
Guinness World Records: "The Corinth Canal, Greece, opened in 1893, is 6.33 km (3.93 miles) long, 8 m (26 ft) deep and 24.6 m (81 ft) wide at the surface and has an extreme depth of cutting of 79 m (259 ft). It is still in use today."
From Wikipedia:
"The Corinth Canal is a canal that connects the Gulf of Corinth with the Saronic Gulf in the Aegean Sea. It cuts through the narrow Isthmus of Corinth and separates the Peloponnesian peninsula from the Greek mainland, thus effectively making the former an island. The canal is 6.3 kilometres (3.9 mi) in length and was built between 1881 and 1893.
Achievement
The Corinth Canal is considered a great technical achievement for its time. It saves the 700-kilometre (430 mi) journey around the Peloponnesus for smaller ships, but since it is only 24 metres (79 ft) wide it is too narrow for modern ocean freighters. The canal is nowadays mostly used by tourist ships; 11,000 ships per year travel through the waterway. The water in the canal is 8 metres (26 ft) deep. At the maximum, the walls are 52 metres high.
At each end of the canal, seashore roads cross using submersible bridges that are lowered to the canal bottom to allow maritime traffic to pass.
Geology
The canal was cut through heavily faulted sedimentary rock in an active seismic zone. Between 1893 and 1940, it was closed for a total of four years for maintenance and to stabilise the walls. In 1923 alone, 41,000 cubic meters of material fell into the canal, which required two years to clear out."