Montana and PPL, a hydroelectric company, are fighting over who owns the rights to Montana's largest river beds.

The Montana Supreme Court decided that PPL owes the state more than $40 million in back-rent for using land under the dams on the rives like the Clark Fork and Missouri.

PPL appealed and now the U.S. Supreme Court will make a decision that could decide property rights beneath streams and rivers across the country.

David Hoffman of PPL Montana says the Clark Fork and Missouri rivers couldn't be navigated at the time of Montana's statehood in 1899, so Montana shouldn't be the one managing the rivers.

"A lot of the arguments are going to revolve around the interpretation of the Lewis and Clark journals...Lewis and Clark did have to get out of the water and portage for nearly a month." Hoffman says this is evidence the rivers were not navigable.

But for the Director of "Montana Trout Unlimited", Bruce Farling, it's a different story, he says the rivers can be navigated, and the state has right to claim the waterways.

"It makes no difference, you can go up to the falls, you can portage around and then keep going. It's a brief interruption for traffic on the river," Farling said.

PPL Montana owns and operates 11 hydroelectric dams in the state, on some of the largest rivers in Montana. One on the Clark Fork River at Thompson Falls and seven on the Missouri river. The state's asking them to fork up rent, more than $40 million, money Farling says the state's entitled to, as owners of the rivers.

"It's beneficial for the state of Montana owns these riverbeds as much as we have claimed historically," Farling said.

But Hoffman says for Montana it seems like it's only about the money, not the rights.

"If the state wins is create a new source of revenue, that is the rent to be collected from persons who occupy these stream beds," he said.

Farling disagrees, he says the rights make it easier for conservation groups like his to make decisions.

"It allows Montanans to have more say on how riverbeds are managed, it's a lot easier to deal with the state then it is with a private party," he said.

But in the end, it's up to the U.S. Supreme Court to decide, they'll hear arguments starting Wednesday. A decision isn?t expected until 2012.

For more information on the case click here.