Yesterday the four tribes were dancing and chanting again. This time, though, on an Edinburgh pavement, far from their California home.

As shareholders piled into ScottishPower's AGM, the four tribes of the Klamath river, in traditional dress, sang and danced before them. It was the latest round in a battle to shame one of Britain's most successful companies into being more environmentally responsible.

The Klamath tribes have already lodged a $1bn (£545m) lawsuit in the US courts against PacifiCorp, a subsidiary of ScottishPower, alleging that the company's dams have destroyed the Klamath's fish population and wiped out some species. But yesterday they opted to embarrass the parent company.

"I have travelled all this way because the dams mean that I have never been able to see a salmon in my part of my river. They have denied me my birthright," said Gail Hatcher, from the Klamath tribe.

The Klamath river, which snakes from Oregon into California, is central to the religion, philosophy and daily lives of the river's four tribes: the Karuk, Yurok, Hoopa and Klamath. For more than seven millennia, native Americans have used the Klamath for worship, healing and food. But since the first dam was built in 1916, the river's ability to provide food and spirituality has dwindled. Now its tribes are fighting back.

"We evolved around the river, so everything around us - our religion, our philosophy our food - is connected to that place," said Leaf Hillman, vice-chairman of the Karuk tribe. "We have lived there since time began, and so have the fish. Our dependence is reciprocal. The fish and the river have provided for us for all those years. Now it is our turn to pay them back."

Before the first dam was built on the Klamath, about 1 million salmon would return to it from the Pacific each year to spawn. Today a return of 100,000 fish is considered a good year.

Although the Klamath's tribes say that fish populations have been dwindling since the construction of the first dam, the devastating decline came in the 1960s, when the final dam was built. It was then that the tribes had to stop their spring ritual; there were no salmon to welcome home.

"When I was young we would catch 100 lampreys in a night," said Mr Hillman. "Now if a fisherman catches 100 lampreys in a season it is considered good. It is not just the salmon that are affected, it is all the fish."

Some 10,000 Native Americans still eke out a living on the Klamath. Tribal elders estimate that 40% of them live below the poverty line. When the fish stocks decline they can go hungry.

The tribes say the way the dams have been managed in recent years is having an increasingly detrimental effect. In 2002 a combination of drought and water management saw 33,000 fish die in the Klamath.

The tribes decided to slap their lawsuit on PacifiCorp and ScottishPower after the company reneged on an agreement to place fish ladders on the Klamath. Federal licences to run the dams are currently up for renewal and, mindful of the tribes' lobbying power, PacifiCorp agreed to install the fish ladders. Then it changed its mind and offered to catch the salmon downstream and transport them up the river.

"They wanted to catch them and truck them up-river. It's laughable," said Jennifer Miller, from the Klamath tribe.

In truth, the tribes' lawsuit probably has little chance of success. In recent years there have been four separate actions against utility companies by Native American tribes. On each occasion, the courts have found for the power company. But the dispute is proving hugely embarrassing. The dams produce 150MW of electricity, only 2% of PacifiCorp's output.

Leaders of the tribe met with ScottishPower's board of directors on Thursday, and were yesterday allowed to speak at the company's AGM. A company spokesman said: "We held constructive talks on a very complex subject."

The tribes are hoping for progress. Mr Hillman said: "They told us we did not need to come. But for decades they have ignored us. Maybe now they will listen." #