While lower Kenai Peninsula streams may be frozen over now, their increasingly warm temperatures during the summer may cause problems for fish spawning, scientists say.

According to a joint study released Monday by the Homer Soil and Water Conservation District and Cook Inlet Keeper, stream temperatures in local streams have exceeded Alaska Department of Environmental Conservation standards for salmon protection in each of the last six years. These increases also are occurring earlier in the year and more often, the report says.

In 2005, for instance, temperatures in the Ninilchik River, Deep Creek, Stariski Creek and Anchor River watersheds exceeded the state’s standard for water temperatures (55 degrees) in spawning areas on more than 80 days.

Also during that year, temperatures on each stream climbed above 68 degrees at one time or another — a level, according to state standards, that “shall not be exceeded.”

Tim Stevens, the DEC environmental program specialist for Southcentral Alaska, said the state guidelines are conservative, but the trend is worrisome.

Warm water makes the fish sluggish and may cause fry to hatch earlier in the year, when there isn’t any food available, he said.

So far, however, the increased temperature hasn’t hurt returns.

Salmon returns at the Anchor River, for instance, have been higher than expected, said Nicky Szarzi, area fish and game biologist for the state.

“And good numbers of smolt are leaving the rivers as well,” she said.

The study was the first comprehensive look on stream temperature on the lower Kenai Peninsula, and historical data is hard to come by, said Sue Mauger, stream ecologist for Cook Inlet Keeper and the author of the report.

“It’s one of the few data sets out there showing a change in temperature,” Mauger said.

Factors identified in the report that could lead to warming include the floods in the fall of 2002, and a combination of warm summers and low snow pack near the headwaters.

Most fishermen on lower Kenai Peninsula streams have noticed unseasonably low water conditions. And these low water conditions and flood-exposed gravel bars can work together to raise water temperatures, Stevens said.

DEC is watching these rivers closely, regardless of why they are warming, Stevens said.

“We’re kind of stumped,” Stevens said. “We don’t know where to go from here.”

With data showing a temperature increase now in the books, the next step is going to be to try to determine a cause, said Mauger. She will spend next summer trying to determine what part of the increase is caused by land use development and what part is natural forces, like climate change.

Logging, road building and gravel pit operations can all raise water temperatures in a watershed, the report said.

At this point, no direct cause for warming has been determined. But the data shows area waters are heating up. What this will mean for future salmon returns is anyone’s guess.

“Part of the temperature story is that there is stress in these systems,” Mauger said. “The systems are changing.”

Ben Stuart can be reached at ben.stuart@homernews.com.