Why is it difficult for a fireman to hold a hose pipe, which ejects a large amount of water at a high velocity?

When fireman directs a large amount of water at a high velocity on fire from a hose pipe, they have to hold the hose pipe strongly because of its tendency to go backward, and hence it becomes difficult to hold. The backward movement of the hose pipe is due to the backward reaction force of water rushing out through it in the forward direction at a high speed as per the Newton's third law of motion.