Some of the most magnificent national parks of the Southwest owe their rugged beauty to the Colorado River and its tributaries.

Unfortunately, dams that have sprung up along the river have changed the water flows in a way detrimental to these national parks, according to a report from the National Parks Conservation Association.

Dinosaur National Monument, Black Canyon of the Gunnison National Park, Canyonlands National Park, Grand Canyon National Park, Glen Canyon National Recreation Area, and Lake Mead National Recreation Area all have been carved to varying degrees into the landscape by the river, and continue to be massaged by the flow of water.

But the series of dams that interrupt the Colorado River in its flow from the high country of Rocky Mountain National Park down to the Gulf of California has altered nature by constricting high runoff flows, artificially enhancing low flows, changing sedimentation patterns, and even impacting water temperatures to the detriment of native fisheries, says the report, National Parks of the Colorado River Basin, Water Management, Resource Threats, and Economics.

Concern over the Colorado has been high in the past year, with at least two books, Running Dry, a Journey from Source to Sea Down the Colorado and The Colorado River: Flowing Through Conflict, examining the struggles the river basin has endured when it comes to appropriation of its waters.

In Running Dry, author Jonathan Waterman traveled the Colorado River's 1,450 miles from its headwaters to the Mexican delta, taking time along the way to point out the too many diversion ditches, dams, and irrigation projects that suck constantly, and increasingly in some areas, from the Colorado.

NPCA's report builds on these narratives, understandably with a bent towards how national parks along the river's path are impacted by the dams that have been built. In the 76-page report the park advocacy group points to a number of findings:

* Large dams in the Colorado River Basin have had and continue to have significant and far-reaching impacts on natural and cultural resources in national parks along the Colorado River and its tributaries. Because of these dams, rivers are now characterized by highly unnatural flow regimes rather than natural hydrological cycles.

* Dams fragment the Colorado River system and interfere with natural ecological processes in national parks.

* Dams and reservoirs have profoundly changed the appearance and sounds of the Colorado River and several of its major tributaries as they flow through national parks.

* Changes in river temperatures and habitats wrought by dams have contributed significantly to declines in native fish populations.

* Dams affect prehistoric and historic cultural resources within national parks.

As a result of dams, how visitors experience them is changed, the group says. For instance, the existence of Flaming Gorge Dam upstream of Dinosaur National Monument controls the Green River to such a degree that, "The deafening roar of the spring flood through the Canyon of Lodore in Dinosaur National Monument is subdued to the point that the sound no longer conveys a sense of the power that created this very place."

At Grand Canyon National Park, of course, the existence of the Glen Canyon Dam just upstream has greatly subdued peak flows that once reached 120,000 cubic feet per second and higher, and led to issues with sandbar creation and fisheries impacts, the report notes.

In Black Canyon of the Gunnison National Park, riparian areas that normally would not be allowed to form due to scouring by spring runoff have developed, says the report.

And, of course, the Glen Canyon Dam has created Lake Powell, a manmade reservoir that has inundated many culturally rich and scenically beautiful side canyons.

Despite recognition from Maj. John Wesley Powell back in 1879 that there was too little water in the West to support large populations, the country's ever-constant expansion has created insatiable, and perhaps unreasonable, demands on the Colorado to nourish communities and crops and to generate hydropower.

These competing demands, of course, are behind the dams and diversions that are targeted in NPCA's report for the problems they've created for the national parks.

Dams within the Colorado River Basin have changed ecological and environmental processes—in many cases quite fundamentally—within Dinosaur National Monument, Black Canyon of the Gunnison National Park, Canyonlands National Park, Glen Canyon National Recreation Area, and Grand Canyon National Park by inundating and destroying natural habitats in some areas, creating highly unnatural flow regimes, trapping sediments that are critical for building and maintaining aquatic and riparian habitats, and altering natural water temperatures that fostered native fish communities. As a result of dam operations, spring floods no longer occur as they once did, peak river flows have decreased while flows during non-peak periods have increased, sediments no longer replenish riverbeds, and water temperatures are generally colder and no longer follow seasonal variations. Cultural resources have also suffered due to dams, with some resources being inundated as reservoirs filled, while others are affected by the same changes in flows and sediment supplies that harm natural resources.

How do we fix it? Can we fix it?

The staff and researchers who put together NPCA's report are optimistic, though it will no doubt require both cooperation and compromise; the longstanding difference of opinion between the National Park Service and U.S. Bureau of Reclamation over high-flow releases from the Glen Canyon Dam is evidence of how difficult it can be to get federal agencies to agree on something.

And then, of course, there's the issue of climate change and how it will impact the river basin and its available waters. As the Interior Department pointed out in another new report issued this past week, stream flows will decrease by 8.5 percent by 2050 while temperatures will increase 5-6 degrees Fahrenheit, a nasty combination that likely will raise tensions over how to allocate scant water resources.

Against this backdrop, the NPCA report recommends a number of steps that can both help the parks and better manage water resources:

* Dam operations should be modified to ensure the National Park Service can achieve its mandate to protect natural and cultural resources in the national parks of the Colorado River Basin.

* Research and monitoring are needed to comprehensively understand natural and cultural resource conditions in the national parks within the Colorado River Basin.

* National parks need additional support to minimize vandalism and unintended resource damage within the Colorado, Green, and Gunnison River corridors.

* Agencies must determine responsibility for management of cultural resources exposed when reservoir levels drop at Glen Canyon National Recreation Area.

* Additional research is needed to comprehensively estimate the economic values provided by national parks along the Colorado River and its tributaries.

* Dam operators, resource managers, and stakeholders basin-wide must adopt a broad perspective, commit to informed and adaptive decisions, and cooperate with one another to successfully address concerns and meet various needs for resource protection, water delivery, flood control, and hydropower generation.

The question, of course, is whether the collective will exists to take these steps?