The owners of large vessels need to investigate relevant regulations before purchasing commercial watercraft insurance. The Maritime Executive recently featured an article about the use of ballast water treatment systems, or BWTS, and whether they are needed in larger ships.
According to this piece, there's an important distinction to be made, depending on the way that boats store and deploy ballast water. If they are "not designed" to do this, or keep water "permanently ballasted," then requirements like those from the United States Coast Guard and the New York Department of Environmental Conservation may not apply.
However, the source does note that this can vary from state to state and that the International Marine Organization, while a sounding board for US policy, has its own regulations. Ship paths, the amount of time they spend holding water and where they discharge it can all change depending on the route.
In the USCG's FAQ on the subject, last updated in April 2013, the role of "economic exclusive zones" (EEZ) and "captain of the port" COTP zones are brought into play: these areas are used to define classes of vessels based on their size and the length of journey.
"Prior to being required to meet the ballast water discharge standard, a vessel using ballast water exchange as its management method arriving to a US port or place after operating outside the EEZ and intending to discharge ballast water taken on from (or mixed with) waters outside the COTP zone of arrival is required to have conducted ballast water exchange."
A BWTS might not be required for vessels that take in high quantities of water, but these regulations could have other specific points (like the amount of living organisms in discharged water) that boat managers should pay attention to.