Representative Kirk (R-IL) introduced a bill (H.R. 801) to amend the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 to require application to all vessels equipped with ballast water tanks, including vessels that are not carrying ballast water, the requirement to carry out exchange of ballast water or alternative ballast water management methods prior to entry into any port within the Great Lakes
, and for other purposes. Text of this bill is not yet available, but the description seems to indicate that a ship fully loaded with cargo, if bound for the Great Lakes, might have to take on and then discharge ballast water on the high seas. But, if the ship is already fully loaded, taking on ballast water might make the ship too heavy and thus unseaworthy.
Source: HK Law