Why do they have dykes in Holland?

Answer 1

Because Holland is lower than the sea level, we have dykes to keep Holland from flooding.

Though it is said that the sea level is going to be more high in 15 years or something.

Eventually, Holland will flood.

Answer 2

It uses dikes to hold back the water due to the fact much of the country is below sea level.

Answer 3

Because the Netherlands is low-lying country - below sea level. The dykes prevent sea water from overwhelming the land.