The idea is to make sure that impacts like discharges from water treatment plants and urban runoff don’t kill fish, or impair their ability to reproduce.

Temperature standards are important because the body temperature of fish basically matches the temperature of the surrounding water, said U.S. Geological Survey research biologist Andrew Todd.

Trout and other species have evolved and spawn under very specific temperature conditions and don’t have a mechanism to adapt to temperature changes in the short-term, Todd said, speaking Wednesday during a water quality summit in Breckenridge.

“When we introduce heat, we disrupt metabolic and reproductive functions,” Todd said.

A number of factors can affect stream temperatures, including sunshine, shading from stream-side vegetation, stream flows and water quantity, as well as direct discharges from point sources like factories and treatment plants.

The latter are less of a factor in the High Country, but increased urbanization around local streams and runoff from paved areas, as well as diversions for snowmaking and other needs, could conceivably influence water temperature in Summit County.

The biggest wild card in the deck is air temperature, which is beyond human control.

Given recent climbing temperature trends associated with climate change, it’s not clear how the state’s new rules will be effective in stemming any potential impacts from global warming.

But as they now stand, the temperature standards are stringent enough to protect even cutthroat trout, most sensitive of the trout species.

“Cutthroat trout drove the setting of the table-value standards,” Todd said, adding that 85 percent of the state’s cold-water streams qualify as cutthroat trout habitat.

Todd explained that the existing standards, set in 1978, were not considered to be scientifically defensible, and that the rules lacked any clear mechanism for enforcement and implementation.

The new temperature limits were determined after scrutinizing hundreds of scientific studies based mainly on laboratory work.

Todd said the rules include criteria for acute conditions (peak temperatures that can kill fish within days), and for chronic conditions — warm temperatures that, over a longer period, can impair reproduction and growth.

The limits also take into account seasonal spawning requirements and are broken down for different types of fisheries, from high mountain trout streams to lowland ponds and rivers with habitat for completely different species.

The rules cover eight cold-water species and 43 warm-water species.

Even these new protective limits may not be adequate to fully protect the resource in the long run, Todd said, explaining that the rules, for example, don’t cover thermal shock, a very sudden change in temperature that can kill fish in a short time.

The state may address that issue during a future round of rulemaking in 2010, he concluded.

The Breckenridge conference included tours of local river restoration projects, streams impacted by mine drainage and other presentations on watershed planning and water quality.

It brought together groups like the Colorado Watershed Assembly, the Colorado Watershed Network and the Colorado Riparian Association.

Local activist Sandy Briggs said the conference was a great networking opportunity, and that he was surprised that no local government officials attended, as far as he knew.

A presentation Tuesday evening by Rocky Mountain Regional Forester Rick Cables focused on the important role of forest health in watershed protection, a crucial issue in Summit County’s beetle-stricken and potentially fire-prone forests.