We talk a lot here about unintended consequences of what people do, or what policy makers decide (we like to call the unintended consequences 'externalities' to make us sound smart). Most of the time these unintended consequences are negatives--or costs: like pollution. But sometimes, a policy might actually create unintended benefits. Here's an example:
"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 [a stop] to that as the water released into the river from the artificial depths of the dam was much colder than normal.[...]
So in 1989 Oklahoma wildlife authorities decided to replenish the depleted fishery with species that thrive in cold water conditions: rainbow and brown trout.
I'm not going to try to argue that the net benefits of the dam are positive, because I don't know. But the dam has created recreational opportunites that otherwise wouldn't have existed and the fish folk are willing to reluctantly admit that:
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.
