What is the Euripus tide phenomenon?

Chalkida sits where the island of Evia almost touches the mainland — across a strait so narrow that the city has been bridged since antiquity. The strait is called the Euripus, and the water that flows through it does something no other Greek waterway does: it reverses direction approximately every six hours.

Stand on the Old Bridge at the wrong hour and the water below races south. Stand there an hour later and it is dead still — what locals call the still water moments. Stand there another hour and the same water is racing north, this time hard enough that small boats wait for slack tide before crossing.

The phenomenon has fascinated travellers since antiquity. Aristotle is supposed (legend says) to have thrown himself into the strait in frustration at not being able to explain it. The actual mechanism — a complex interaction between Aegean and North Aegean tides amplified by the bottleneck of the strait — wasn't properly understood until the twentieth century.

What it means in practice: most days, the current reverses four times. Some weeks the reversals are 'regular' — every six and a quarter hours, the textbook pattern. Other weeks the strait goes 'irregular' — periods of confused tides that can last for days. There is a small museum on the bridge that explains the mechanism for those who want the science.

From a guest's point of view, the question is simply when to be on the bridge. Locals hold to the rule that the most dramatic moments are at sunrise and sunset reversals — the water turning copper as the city's lights come on, fishing boats running fast with the current. From the planned Chalkida house, the Old Bridge is two minutes' walk. Plan dinner near the strait; time it for the turn.