A federal appeals panel has rejected a request by five Great Lakes states for an immediate order to close shipping locks on Chicago-area waterways and take other steps to prevent Asian carp from invading Lake Michigan.

The three-judge panel of the 7th U.S. Circuit Court of Appeals ruled Wednesday against the request by Michigan, Minnesota, Ohio, Pennsylvania and Wisconsin for a preliminary injunction. The states were appealing a decision by a federal district judge to deny their request last December.

The states have a pending lawsuit that calls for closing the locks and quickening an Army Corps of Engineers study of whether to permanently sever the man-made link between the Great Lakes and Mississippi River basins.

They claim that the Metropolitan Water Reclamation District and the U.S. Army Corps of Engineers are operating the waterways in a manner that will increase the likelihood that Asian carp will be able to make their way into the Great Lakes.  They insist the locks could provide a pathway for the carp to invade the lakes and disrupt the food web.

While the three judge panel agreed with a district judge’s earlier decision to deny the immediate closure, they differed in their assessment of the overall situation.

“We are less sanguine about the prospects of keeping the carp at bay,” wrote Judge Diane Wood on behalf of the panel.  “In our view, the plaintiffs presented enough evidence at this preliminary stage of the case to establish a good or perhaps even a substantial likelihood of harm – that is, a non-trivial chance that the carp will invade Lake Michigan in numbers great enough to constitute a public nuisance.”

Furthemore, the court agreed that if the carp do enter Lake Michigan “there is little doubt that the harm to the plaintiff states would be irreparable.”

However, the court determined that the evidence didn’t constitute sufficient grounds to force an immediate closure, noting that the defendants and a range of federal and state agencies “have mounted a full-scale effort to stop the carp” and have promised to take additional steps to do so.

Nevertheless, the three judge panel confined their ruling to the situation at hand - noting that if circumstances change, there could be grounds to reconsider the request for an immediate closure.