Which waterway separates the Peloponnesus from mainland Greece?

The Corinth Canal cuts through the narrow Isthmus of Corinth and separates the Peloponnese from the Greek mainland, arguably making the peninsula an island. The canal was dug through the isthmus at sea level and has no locks. It is 6.4 kilometres (4 mi) in length and only 21.4 metres (70 ft) wide at its base, making it impassable for many modern ships. It is currently of little economic importance becoming mainly a tourist attraction.

The canal consists of a single channel 8 metres (26 ft) deep, excavated at sea level (thus requiring no locks), measuring 6,343 metres (20,810 ft) long by 24.6 metres (81 ft) wide at sea level and 21.3 metres (70 ft) wide at the bottom. The rock walls, which rise 90 metres (300 ft) above sea level, are at a near-vertical 80° angle. The canal is crossed by a railway line, a road and a motorway at a height of about 45 metres (148 ft). A highway crossing the canal connects Athens and the Peloponnese.