Ballast water is water taken on board ships to provide stability and balance while they are at sea. It is usually stored in tanks and can be adjusted depending on the ship's load and the conditions of the ocean. This water is essential for safe navigation, especially for large vessels like cargo ships and tankers. However, when ships take on ballast water in one location and discharge it in another, they can unintentionally introduce non-native species into new environments. This can disrupt local ecosystems and harm native species, leading to significant ecological and economic consequences.