Zebra mussels have been a scourge in the Great Lakes since being brought in by ships in the late 1980s. NOAA Great Lakes Environmental Research Laboratory/D. Jude, Univ. of Michigan/Flickr

Round gobies, alewives, sea lampreys, Pacific salmon, zebra mussels, and quagga mussels are just some of the 180 invasive species in the Great Lakes. A few, like the salmon, were introduced intentionally. Most others, though, sneaked their way in through the ballast water that’s used to balance ships hulls. They come from the Atlantic Ocean or the Black or Caspian Sea, or perhaps the Dnieper River in Eastern Europe. But now these critters are here, settling in and exacting enormous harm on the the lakes' freshwater ecosystem.

Like those invasive species stowing away in ships, representatives in Congress recently slipped a provision into this year’s National Defense Authorization Act that would weaken current shipping rules. The provision’s proponents want the Coast Guard to be the sole agency overseeing ballast water, thereby taking the U.S. Environmental Protection Agency and the Clean Water Act out of the regulatory equation. The House passed the bill on May 18, and if the Senate's version or the final defense bill ends up including the same language, the Great Lakes should brace for more invasions.

“If Congress locks in a weak ballast water standard, we'll have more invasive species in the future, and we’ve already had too many,” says Rebecca Riley, a senior attorney at NRDC, which publishes onEarth. “The way to keep them out of our lakes is to make sure discharged ballast water is as clean as it can be.”

The Clean Water Act currently requires ships to use the best technology available to clean ballast water. But environmentalists argue that the EPA could be doing an even better job of enforcing the law. Last year, environmental groups, including NRDC, sued the agency over ballast regulation they felt was too lax. A federal court agreed. The judges said existing technologies including water filtration or treatment with ultraviolet light or chlorine—ones the EPA didn’t consider—could also be used to kill invasives before vessels dump their liquid loads. If ships are exempt from the Clean Water Act, they won't have to keep up-to-date with the best methods of ridding ballast of lurking organisms.

The EPA isn't the only federal agency currently regulating ballast water; the other is the Coast Guard, which which enforces the National Invasive Species Act. State agencies also have their own laws. This has prompted the shipping industry to say that the various laws are too hard to follow. In an effort to streamline the process, members of Congress, such as Florida Senator Marco Rubio and Representative Duncan Hunter of California, want to excuse the ships from abiding by the Clean Water Act (and therefore EPA oversight).

The members of Congress saw the bill as an opportunity to include unrelated clauses, Riley says. The defense bill is must-pass legislation, so the unpopular provision just may have a shot at getting through. That’s why NRDC and other environmental groups, such as the National Wildlife Federation, are bringing attention to the add-on. The White House has also come out against the ballast water provision, saying it "undermines the ability to fight the spread of invasive species."

Scientists agree. Ed Rutherford, a fisheries biologist with NOAA’s Great Lakes Environmental Research Laboratory, says the country has already spent millions of dollars on measures to mitigate the effects of invasives, from attempting to eliminate mussels to testing traps for sea lampreys. Relaxing the rules could begin to undo that progress. From the 1950s to the 1990s, the lakes saw an average of two invasive species a year. When lawmakers started closing loopholes in existing regulations—for example, requiring seafaring ships (known as salties) to use saltwater to shock and kill any would-be freshwater stowaways in their tanks—the number of yearly invaders fell to zero. Scientists have seen no new invasions attributable to ballast water since 2006.

But there’s still room for improvement. No monitoring program exists to detect invasives, argued George Meyer of the Wisconsin Wildlife Federation and NWF’s Marc Smith in a 2014 op-ed in the Milwaukee Journal Sentinel. They pointed out that when scientists did go looking for invaders in the St. Louis River and Duluth-Superior Harbor, they found eight. If anything, Meyer and Smith argue, laws need to be stricter.

“Anything that’s less stringent than the current regulatory framework would be damaging,” says Rochelle Sturtevant, an educator at the Great Lakes Environmental Research Laboratory who has been working on the biological makeup of the lakes for more than two decades. To her, fellow scientists, and environmental groups, the provision is just another unwanted and destructive invader—something defense bills should protect against, not invite in.

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.