Throughout most of human history, water transportation was the only way to move large loads over long distances.
Today there are other choices, but water transportation is still the least expensive.
Many tons of bulk material such as ore, coal and grain are moved by water each year. Water transportation on a large scale, requires a large amount of construction on and off shore. Channels and port facilities have to be built and maintained, and land-based storage and transportation needs to be readily accessible. Each of these has an effect on the coastal environment. If dumped in the water, it can cover bottom dwelling organisms and muddy the water.