A federal judge in Detroit on Thursday dismissed a lawsuit by shipping companies who sought to overturn a Michigan law requiring them to clean ballast water. That water is the source of many invasive species which have entered the Great Lakes, notably the zebra mussel.

Although the U.S. Coast Guard requires oceangoing ships to change ballast water while still at sea and bound for U.S. ports, ships declaring they are carrying no ballast water must perform only recommended best practices to rid their ballast tanks of residual water and organisms. Starting in January, the state of Michigan required shippers to obtain permits before entering state ports. The permits verified that ships either wouldn’t discharge ballast water or that crews would use only state-approved, environmentally sound techniques to cleanse ballast water.

Shipping interests challenged the law, saying it violated other Michigan laws, pre-empted federal law, discriminated against them as out-of-state businesses and violated their constitutional rights.

Federal Judge John Feikens wrote in his decision that federal courts are prohibited from ruling on state laws. He also wrote that the state didn’t pre-empt federal laws, that it is perfectly reasonable for the state of Michigan to pass its own law and that the shippers didn’t show any harm from discrimination. He dismissed the suit with prejudice, meaning the plaintiffs cannot bring another legal action on the same claim.