Flathead Lake is still among the cleanest large lakes in the world, but increased pollution and rising temperatures paint an uncertain future, according to Dr. Jack Stanford of the Yellow Bay Biological Station.

Stanford delivered his annual "State of the Lake" address to the Flathead Lakers last Thursday evening at Flathead Lake Lodge, where he reported that residents are experiencing a particularly clear look into the Lake's depth this summer.

"The Lake is really clean and clear this summer," he told the crowd of more than 150 people. "There is nothing unusual I can report to you."

Stanford said that as of earlier last week the Lake showed a secchi disk measurement — essentially a shiny plastic disk that's lowered until it cannot be seen from the surface — was about eight meters. He said that by fall, that depth would be closer to 10 meters.

But while the water is clear, it is not completely clean. Stanford said that though phosphorous levels have been in steady decline for years, nitrogen levels have risen as more people come to the Valley. Both of those substances encourage the growth of pollution algae.

Stanford said that increasing numbers of septic systems upriver and around Flathead Lake contribute to some nitrogen loading, about 30 percent of the nutrients in the Lake come from the air.

In addition to nutrients that encourage algae growth, Stanford also reported that the Lake has steadily warmed since 1990.

The station's research has shown a steady increase in the depth of the mix layer where sun-warmed water and cold deep-lake water meet in the water column.

"There's nothing we can do about it," Stanford said. "It's just a manifestation of global warming."

Not only does more and deeper warm water create a more inviting environment for algae and invasive species like zebra mussels, it also prevents the Lake from freezing over completely in the winter, something that hasn't happened since 1988.

"Flathead Lake is like a canary in a cave," Stanford said. "We can tell by the depth of warm water and comparisons and really calibrate this climate warming phenomenon."

Stanford made multiple references to coal mining proposals in British Columbia, Canada, upriver from Flathead Lake.

"The bottom line is that what happens upriver influences water quality," he said. "Luckily, upstream is Glacier Park and the Bob Marshall Wilderness. Sixty-seven percent of the water in the Lake is from protected areas."

Stanford called the potential mining operations the biggest threat to Flathead Lake and urged the Lakers to be vigilant and outspoken on the subject.

But the news was far from all bad in Stanford's much anticipated yearly update. The crown jewel of the Flathead is still pretty well off.

"There have been no big changes since 1990 in primary production (of algae)," Stanford said. "That means, quite profoundly, that best management practices in the basin are working."

Stanford recalled first arriving at the biological station in 1971 and marveling at the transparency of the water near Blue Bay to the point that he almost wrecked his old Jeep.

That fascination, he said, remains today.

"I just can't believe it's that transparent," he said. "Let's keep it that way."