Hydropower dams are unpopular with conservationists because they disrupt river ecosystems, kill spawning fish populations, and release large amounts of methane from decaying vegetation along riverbeds.

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Such flow levels were a reproductive cue for spawning fish and produced sandbars that served as vital nesting grounds for shorebirds, particularly the least tern and piping plover.

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The treaty said that each was entitled to a catch proportionate to the numbers of fish spawning in its own rivers.

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And while the projects are usually sited away from fish-spawning grounds, aquatic life still can get trapped behind the weirs or at the mouth of the penstock.

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But every day, hundreds of ASF volunteers battle for the species on the ground, rebuilding and restoring river and fish-spawning habitat in the Atlantic Canada provinces and Maine.

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But she noted that with the spill moving toward land, the impact on Louisiana's coastline, which contains some 40% of the nation's wetlands and spawning grounds for countless fish and birds, had to be considered.

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Thames Water had initially looked at draining the lake to make the repair but this was ruled out as the fish are in spawning season.

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Removing the dam restored 17 miles of prime spawning and rearing habitat for migratory fish, and re-established numerous rapids for more recreation.

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Immediately, salmon spawning began to recover and according to the Oregon Department of Fish and Wildlife, for some varieties is now at the highest levels since at least 1950, as measured in naturally produced adults.

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But dams, diversions and recent drought have combined to push the spawning salmon population in the Klamath well below the 35, 000-fish threshold deemed necessary for the river to maintain a sustainable salmon population.

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"There's an awful lot of fish in Tweed and now the urge to get up into the spawning grounds is increasing, " said Mr Yonge.

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