The U.S. Coast Guard and Canadian regulators say they inspected the ballast tanks of all 466 saltwater ships that entered the Great Lakes in 2016, a measure that has been credited with reducing new invasive species in the lakes.

The agencies reported this week that they assessed all 8,488 ballast tanks on the ships to make sure they complied with orders to "swish and spit" their ballast tanks - flushing the tanks at sea in an effort to kill any freshwater organisms that might be inside.

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Ballast inspections have been mandatory since 2006 for ships entering both the U.S. and Canadian waters of the Great Lakes, and this is the seventh consecutive year the Coast Guard has claimed 100 percent inspection of the saltwater ships.

It's those ships that, in the past, were blamed for bringing dozens of foreign aquatic species into the Great Lakes where they have escaped to wreak havoc - including zebra and quagga mussels, spiny water flea, ruffe, goby and the fish-killing viral hemorrhagic septicemia fungus.

A decade ago researchers were finding a new species in the Great Lakes on average every 28 weeks, with 185 foreign invaders over the last century, many after the St. Lawrence Seaway opened in 1959. But the ballast flushing and inspections are in large part credited with keeping new species out of the lakes from 2006 to 2016.

That decadelong run ended last summer, however, when a small crustacean from Europe and Asia was discovered in Lake Erie by a Cornell University scientist. Thermocyclops crassus, an invertebrate zooplankton, has probably been in the lake since 2014, the Environmental Protection Agency said in announcing the finding in November.

As of now the critter is not expected to cause ecological harm in the Great Lakes. It's considered foreign but not invasive, meaning it's not likely to explode in number.

"The best data we have is that in Lake Champlain, where it's been since 1991, it hasn't been invasive. It hasn't exploded in range or number, and we don't think it will in the Great Lakes, either," said Doug Jensen, invasive species expert for Minnesota Sea Grant. "So we've still got a pretty good string going in shutting down the pathways for new invasives."

The new ballast water inspection report was released by the Great Lakes Seaway Ballast Water Working Group includes U.S. Coast Guard, U.S. Saint Lawrence Seaway Development Corporation, Transport Canada - Marine Safety & Security and the Canadian St. Lawrence Seaway Management Corporation.

Supporters say swish-and-spit is killing up to 98 percent of the freshwater organisms hiding in ballast tanks so few new critters can escape and colonize new waters. But even with swish-and-spit apparently helping, U.S. and Canadian regulators have not backed off requirements for onboard ballast water treatment methods to further protect against any species surviving in ballast tanks.

That next level of protection is on its way for the 12,000 saltwater ships that enter all U.S. waters annually under federal regulations. Globally, the International Maritime Organization is doing the same, through a treaty, although that process has moved much slower with 70,000 ships to deal with.

The onboard systems likely to be approved include chemicals, ultraviolet light, filters or a combination of technologies to kill any critters in the tanks. The goal is to reduce their numbers so much that any survivors couldn't establish a colony in a new port. The on-board rule will be phased in by 2021.

Minnesota and Wisconsin also are looking at freighters that never leave the Great Lakes, noting those boats move millions of gallons of ballast water between infested ports every year and are a likely pathway to spread invaders - especially in and out of Duluth-Superior, by far the busiest of Great Lakes' ports.

Both states have rules on the books to apply the IMO standards to lakers at each boat's first dry-dock after 2018, with all completed by about 2023, unless boat owners can convince regulators that it's not possible.

The first saltwater ship of the season is expected to arrive in the Twin Ports in early April.