It looks like a perfect trout stream in autumn: clear, cold water gushing over rocks and through wooded hills shedding the last of their leaves.
BEAVERS BEND STATE PARK, Okla. — It looks like a perfect trout stream in autumn: clear, cold water gushing over rocks and through wooded hills shedding the last of their leaves.
But while the setting seems natural, the resident trout are not. First introduced 17 years ago to the Lower Mountain Fork River in southeastern Oklahoma, they owe their existence here to an unlikely source: the local dam.
"There was a natural free-flowing warm water stream here that had populations of native sport fish such as smallmouth bass," said Paul Balkenbush, a fisheries supervisor with the Oklahoma Department of Wildlife Conservation.
But the construction of a dam nearby in 1968 put paid to that as the water released into the river from the artificial depths of the dam was much colder than normal.
Deeper water is colder water and the intake to the hydropower turbines is located down in the cooler layer.
"When the water suddenly got colder it displaced the natural warm-water fish that were there," said Balkenbush.
So in 1989 Oklahoma wildlife authorities decided to replenish the depleted fishery with species that thrive in cold water conditions: rainbow and brown trout.
Balkenbush said state scientists viewed the trout as a "surrogate as opposed to an invasive fishery."
Invasive fish -- which are introduced to waters where they are not native -- are considered by biologists to be a pest as they often compete with or prey on local fish. But in this case the indigenous species had already been displaced.
Such inadvertent trout habitat created by dams -- which are usually bad for fish because they cut off migration routes and cause other problems -- are called "tailwaters."
There is no hard data on how many there are in the United States but conservationists and angling associations reckon that there are probably hundreds.
SUPERB ANGLING
Oklahoma now stocks the Lower Mountain Fork with over 100,000 trout each year -- to the delight of anglers who come from near and far.
"There are closer trout waters but it is worth it for me to drive 3-1/2 hours to bring my clients here," said Ken Cole, a Dallas-based fly fishing guide and frequent visitor.
Another angler on the river climbed out of a huge pick-up truck bearing Michigan license plates.
Regulars like Cole are thrilled that the hatchery-reared fish have started to spawn in the river. Last year saw the first documented natural reproduction of rainbow trout in Oklahoma on the Lower Mountain Fork.
"That's one of the 'wild' ones born here," said Cole after a 4-inch baby took a fly in a pool. After a brief struggle it was released back into the water.
The trout fishery is also seen as a boon for the local, rural economy though there are no hard numbers to substantiate this beyond anecdotal evidence and a 1993 survey that found it to be worth $1 million annually at that time.
DAM IT ALL
Most fish biologists see more bad in dams than good -- and the ecological damage wrought on the native fish on the Lower Mountain Fork attest to their disruptive powers.
"I personally spend a lot more time trying to remove dams than thinking about their benefits," said Oregon-based Jack Williams, the senior scientist with conservation organisation Trout Unlimited.
Dams destroy habitat and prevent fish from reaching their spawning grounds. Even artificial fish ladders to help facilitate migration are a poor second to the real thing.
Dams also change water temperature and regulate river levels and flows for agriculture or industry -- all of which can have negative consequences on the local marine life.
Still, some see a new fishery as being better than none at all if a dam is deemed necessary for flood control, water supply or hydro power.
"We generally favour the native fish but we recognise that there are situations where a tailwater fishery can provide recreational and economic benefits," said Williams.
Source: Reuters
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