Ballast discharge is when a ship releases a large amount of water into the ocean (ballast water). When a ship has unloaded its cargo, it takes on ballast (water) to weigh-down the ship in order to keep it stable while it moves between ports or waits for more cargo to be loaded.
Ballast is taken-on by bigger ships like cruise ships, large tankers and bulk cargo carriers. This ballast water usually contains biological materials, plants, animals, viruses and bacteria, algae and other foreign constituents. Because ballast water can be taken from one body of water then moved and dumped at another. This can cause adverse and harmful environmental impacts from depositing foreign materials in a different water sources.
Some harmful examples of ballast disposal are invasive species such as:
North American comb jelly
Toxic algae (red tide/ brown tide).
Many countries have outlined the dangers of ballast water such as:
New Zealand (Biosecurity Act 1993)
United States of America (National Invasive Species Act 1996)
Australia (Biosecurity Act 2015)