There are many folk tales about kappa.
There is a temple in the Asakusa district of Tokyo that is famous for kappa. A man named Kihachi lived near the temple during the Edo period (1603-1868). Kihachi was a seller of raincoats, and his business was thriving. The land in the area was low-lying, however, so he used the money he had earned to begin building flood defenses for the people of the area, to keep out the river water. Some kappa helped him with the work. Because of this, it was said that good things would happen if you saw a kappa.
On the Chikugo river, famous as the longest river on the island of Kyushu in southern Japan, there is a widely known story of how local people used to practice sumo wrestling with kappa. (From a story by Kawano Emiko)
In the town of Shikama in Miyagi Prefecture in northeastern Japan, there is a shrine devoted to a water god. In the Heian period (794-1192), a shogun named Sakanoue no Tamuramaro arrived in this area. A man called Touemon swam like a kappa across the swiftly flowing river and worked hard for the shogun. The shogun was so pleased that he gave Touemon the surname kappa, which has been handed down by generations of chief priests at the shrine ever since.
The kappa's favorite food is the cucumber. In ancient times, some houses had streams running through their grounds for washing vegetables and other things. People would take the first cucumbers harvested and throw them into these streams as offerings to the water god.