Dishwasher spray arms can become clogged for a few reasons. The most common reason is food debris. Over time, bits of food can build up in the small holes of the spray arm and cause it to become blocked. Another reason why dishwasher spray arms might become clogged is because of hard water deposits. If you have hard water, minerals can collect on the spray arm and eventually block it.
If your dishwasher's spray arm becomes clogged, it won't be able to rotate properly and will likely cause your dishes to come out dirty. To clean a clogged dishwasher spray arm, you'll need to remove it from the dishwasher and soak it in vinegar or a similar cleaning solution. Once it has soaked for a while, use a brush to remove any debris that's still stuck in the holes. Then, rinse off the spray arm with water and put it back in your dishwasher.