Utilities seeking to build a transmission line connecting Iowa and Wisconsin are appealing a court decision blocking the Mississippi River crossing and say construction delays could leave the power grid more vulnerable to blackouts, limit clean energy production and lead to higher electricity prices.

Earlier this year, federal Judge William Conley sided with four conservation groups that sued to stop the $492 million Cardinal-Hickory Creek line, finding the environmental review was inadequate and the project is incompatible with the Upper Mississippi River National Wildlife and Fish Refuge.

Conley also ruled that a proposed land exchange cannot be used “to evade Congress’ mandate” for the refuge, which covers 261 river miles between Wabasha, Minnesota, and Rock Island, Illinois.

Attorneys for American Transmission Co., ITC Midwest and Dairyland Power Cooperative have appealed Conley’s decision and asked the appeals court to suspend his order blocking the land swap, which they say will delay the December 2023 completion date.