The Corinth canal in Greece was closed earlier this week after a rockfall blocked the route.
Work to clear the debris is expected to take at least two weeks, officials have said.
The 6.4km canal is used by around 11,000 vessels each year and provides a shortcut from southern Italy to the Eastern Mediterranean and the Black Sea. The alternative route around the Peloponnese is 700km longer. The canal is only 24.6m wide and up to 9m deep.
According to the local coastguard, the rockfall occurred after a period of heavy rain.
The canal has suffered from rockfalls in the past with the most serious in 1923, which resulted in the closure of the route for two years. The canal was also damaged by the Germans during the Second World War and repairs then took five years.