SANDPOINT, Idaho -

An Idaho conservation group is pressing ahead with its lawsuit challenging the Bonneville Power Administration's plan for managing winter water levels in the state's biggest lake.

The Idaho Conservation League initially filed its lawsuit in 2012, but has been unable to reach a settlement with BPA over winter pool levels at Lake Pend Oreille.

The Bonner County Daily Bee reports that ICL renewed its case by filing a brief with the 9th U.S. Circuit Court of Appeals. The conservation group wants BPA scientists to do more rigorous study of its so-called Flexible Winter Power Operations plan.

That plan allows the lake pool to be fluctuated within a five-foot range up to three times each winter to maximize power generation at the Albeni Falls Dam.