High Quality Content by WIKIPEDIA articles! The Intelligent Water Drops algorithm is one of the newly-developed swarm-based optimization algorithms. This optimization algorithm has been inspired from natural rivers. So far, it has been used for a few NP-hard optimization problems such as traveling salesman problem, multidimensional knapsack problem, n-queen puzzle, automatic multi-level thresholding of gray-level images, trajectory planning, robot path planning, and vehicle routing. Numerous actions and reactions happen among water drops of a natural river.