What is the colorful carp banners”that is called Koinibori in Japanese

When I drove my car in the countryside,
I found a lot of “colorful carp banners”that is called Koinibori in Japanese.

We generally celebrate May 5 as “Children’s day”, which is one of Japanese national holidays.
The another name of “Children’s day” is “Boy’s festival”.
“Children’s day” based on “The day for the prevention of cruelty to children” was established in 1948.
Boy’s parents display “colorful carp banners”.
Many people eat some famous sweets to celebrate the special day.
“colorful carp banners” are famous symbol to celebrate “Children’s day”.
Many parents display them hoping that children will grow up with courage and wisdom.